javascript小技巧-js小技巧收集(转)每一项都是js中的小技巧,但十分的实用!
javascript小技巧-js小技巧收集(转)每一项都是js中的小技巧，但十分的实用！
1.document.write(""); 输出语句
2.JS中的注释为//
3.传统的HTML文档顺序是:document->html->(head,body)
4.一个浏览器窗口中的DOM顺序是:window->(navigator,screen,history,location,document)
5.得到表单中元素的名称和值:document.getElementById("表单中元素的ID号").name(或value)
6.一个小写转大写的JS: document.getElementById("output").value = document.getElementById("input").value.toUpperCase();
7.JS中的值类型:String,Number,Boolean,Null,Object,Function
8.JS中的字符型转换成数值型:parseInt(),parseFloat()
9.JS中的数字转换成字符型:(""+变量) 10.JS中的取字符串长度是:(length) 11.JS中的字符与字符相连接使用+号. 12.JS中的比较操作符有:==等于,!=不等于,>,>=,<.<= 13.JS中声明变量使用:var来进行声明14.JS中的判断语句结构:if(condition){}else{} 15.JS中的循环结构:for([initial e-xpression];[condition];[upadte e-xpression]) {inside loop} 16.循环中止的命令是:break 17.JS中的函数定义:function functionName([parameter],...) 18.当文件中出现多个form表单时.可以用document.forms[0],document.forms[1]来代替. 19.窗口:打开窗口window.open(), 关闭一个窗口:window.close(), 窗口本身:self 20.状态栏的设置:window.status="字符"; 21.弹出提示信息:window.alert("字符"); 22.弹出确认框:window.confirm(); 23.弹出输入提示框:window.prompt(); 24.指定当前显示链接的位置:window.location.href="URL" 25.取出窗体中的所有表单的数量:document.forms.length 26.关闭文档的输出流:document.close();
27.字符串追加连接符:+= 28.创建一个文档元素:document.createElement(),document.createT extNode() 29.得到元素的方法:document.getElementById() 30.设置表单中所有文本型的成员的值为空: var form = window.document.forms[0] for (var i = 0; i if (form.elements.type == "text"){ form.elements.value = ""; } } 31.复选按钮在JS中判断是否选中:document.forms[0].checkThis.checked (checked属性代表为是否选中返回TRUE或FALSE) 32.单选按钮组(单选按钮的名称必须相同):取单选按钮组的长度document.forms[0].groupName.length 33.单选按钮组判断是否被选中也是用checked. 34.下拉列表框的值:document.forms[0].selectName.options[n].value (n有时用下拉列表框名称加上.selectedIndex来确定被选中的值) 35.字符串的定义:var myString = new String("This is lightsword"); 36.字符串转成大写:string.toUpperCase(); 字符串转成小写:string.toLowerCase(); 37.返回字符串2在字符串1中出现的位置:String1.indexOf("String2")!=-1则说明没找到. 38.取字符串中指定位置的一个字符:StringA.charAt(9); 39.取出字符串中指定起点和终点的子字符串:stringA.substring(2,6);
40.数学函数:Math.PI(返回圆周率),Math.SQRT2(返回开方),Math.max(value1,value2)返回两个数中的最在值,Math.pow(value1,10)返回value1的十次方,Math.round(value1)四舍五入函数,Math.floor(Math.random()*(n+1))返回随机数41.定义日期型变量:var today = new Date(); 42.日期函数列表:dateObj.getTime()得到时间,dateObj.getYear()得到年份,dateObj.getFullYear()得到四位的年份,dateObj.getMonth()得到月份,dateObj.getDate()得到日,dateObj.getDay()得到日期几,dateObj.getHours()得到小时,dateObj.getMinutes()得到分,dateObj.getSeconds()得到秒,dateObj.setTime(value)设置时间,dateObj.setYear(val)设置年,dateObj.setMonth(val)设置月,dateObj.setDate(val)设置日,dateObj.setDay(val)设置星期几,dateObj.setHours设置小时,dateObj.setMinutes(val)设置分,dateObj.setSeconds(val)设置秒[注意:此日期时间从0开始计] 43.FRAME的表示方式: [window.]frames[n].ObjFuncVarName,frames["frameName"].ObjFuncVarName,frameNam
e.ObjFuncVarName 44.parent代表父亲对象,top代表最顶端对象45.打开子窗口的父窗口为:opener 46.表示当前所属的位置:this 47.当在超链接中调用JS函数时用:(javascript :)来开头后面加函数名48.在老的浏览器中不执行此JS: 49.引用一个文件式的JS: 50.指定在不支持脚本的浏览器显示的HTML: 51.当超链和onCLICK事件都有时,则老版本的浏览器转向a.html,否则转向 b.html.例:dfsadf 52.JS的内建对象有:Array,Boolean,Date,Error,EvalError,Function,Math,Number,Object,RangeError,Refere nceError,RegExp,String,SyntaxError,TypeError,URIError 53.JS中的换行:/n 54.窗口全屏大小: 55.JS中的all代表其下层的全部元素56.JS中的焦点顺序:document.getElementByid("表单元素").tabIndex = 1 57.innerHTML的值是表单元素的值:如"how are you" ,则innerHTML的值就是:how are you 58.innerTEXT的值和上面的一样,只不过不会把这种标记显示出来. 59.contentEditable可设置元素是否可被修改,isContentEditable返回是否可修改的状态. 60.isDisabled判断是否为禁止状态.disabled设置禁止状态61.length取得长度,返回整型数值62.addBehavior()是一种JS调用的外部函数文件其扩展名为.htc 63.window.focus()使当前的窗口在所有窗口之前. 64.blur()指失去焦点.与FOCUS()相反.
65.select()指元素为选中状态. 66.防止用户对文本框中输入文本:onfocus="this.blur()" 67.取出该元素在页面中出现的数量:document.all.tags("div(或其它HTML标记符)").length 68.JS 中分为两种窗体输出:模态和非模态.window.showModaldialog(),window.showModeless() 69.状态栏文字的设置:window.status='文字',默认的状态栏文字设置:window.defaultStatus = '文字.'; 70.添加到收藏夹:external.AddFavorite("https://www.360docs.net/doc/4716194721.html,"t;,"jaskdlf");
71.JS中遇到脚本错误时不做任何操作:window.onerror = doNothing; 指定错误句柄的语法为:window.onerror = handleError; 72.JS中指定当前打开窗口的父窗口:window.opener,支持opener.opener...的多重继续. 73.JS中的self指的是当前的窗口74.JS中状态栏显示内容:window.status="内容" 75.JS中的top指的是框架集中最顶层的框架76.JS中关闭当前的窗口:window.close(); 77.JS中提出是否确认的框:if(confirm("Are you sure?"))else{alert("Not Ok");} 78.JS中的窗口重定向:window.navigate("https://www.360docs.net/doc/4716194721.html,"t;); 79.JS中的打印:window.print() 80.JS中的提示输入框:window.prompt("message","defaultReply"); 81.JS中的窗口滚动条:window.scroll(x,y) 82.JS中的窗口滚动到位置:window.scrollby 83.JS中设置时间间隔:setInterval("expr",msecDelay)或setInterval(funcRef,msecDelay)或setTimeout 84.JS中的模态显示在IE4+行,在NN中不行:showModalDialog("URL"[,arguments][,features]);
85.JS中的退出之前使用的句柄:function verifyClose(){event.returnValue="we really like you and hope you will stay longer.";}} window.onbeforeunload=verifyClose; 86.当窗体第一次调用时使用的文件句柄:onload() 87.当窗体关闭时调用的文件句柄:onunload() 88.window.location的属性: protocol(http:),hostname(https://www.360docs.net/doc/4716194721.html,),port(80),host(https://www.360docs.net/doc/4716194721.html,:80),pathname("/a/a.h tml"),hash("#giantGizmo",指跳转到相应的锚记),href(全部的信息) 89.window.location.reload()刷新当前页面. 90.window.history.back()返回上一页,window.history.forward()返回下一页,window.history.go(返回第几页,也可以使用访问过的URL) 91.document.write()不换行的输出,document.writeln()换行输出92.document.body.noWrap=true;防止链接文字折行. 93.变量名.charAt(第几位),取该变量的第几位的字符. 94."abc".charCodeAt(第几个),返回第几个字符的ASCii码值. 95.字符串连接:string.concat(string2),或用+=进行连接96.变量.indexOf("字符",起始位置),返回第一个出现的位置(从0开始计算) https://www.360docs.net/doc/4716194721.html,stIndexOf(searchString[,startIndex])最后一次出现的位置. 98.string.match(regExpression),判断字符是否匹配.
99.string.replace(regExpression,replaceString)替换现有字符串. 100.string.split(分隔符)返回一个数组存储值. 101.string.substr(start[,length])取从第几位到指定长度的字符串. 102.string.toLowerCase()使字符串全部变为小写. 103.string.toUpperCase()使全部字符变为大写. 104.parseInt(string[,radix(代表进制)])强制转换成整型. 105.parseFloat(string[,radix])强制转换成浮点型. 106.isNaN(变量):测试是否为数值型. 107.定义常量的关键字:const,定义变量的关键字:var --------------------------------------------------------------------------------------------------------------------------------javascript38种小技巧，推荐新手查看。事件源对象event.srcElement.tagName event.srcElement.type 捕获释放event.srcElement.setCapture(); event.srcElement.releaseCapture(); 事件按键event.keyCode event.shiftKey event.altKey event.ctrlKey 事件返回值event.returnValue 鼠标位置event.x event.y 窗体活动元素document.activeElement 绑定事件document.captureEvents(Event.KEYDOWN); 访问窗体元素document.all("txt").focus(); document.all("txt").select(); 窗体命令document.execCommand 窗体COOKIE document.cookie 菜单事件document.oncontextmenu 创建元素document.createElement("SPAN"); 根据鼠标获得元素：document.elementFromPoint(event.x,event.y).tagName=="TD
document.elementFromPoint(event.x,event.y).appendChild(ms) 窗体图片document.images[索引] 窗体事件绑定document.onmousedown=scrollwindow; 元素document.窗体.elements[索引] 对象绑定事件document.all.xxx.detachEvent('onclick',a); 插件数目navigator.plugins 取变量类型typeof($js_libpath) == "undefined" 下拉框下拉框.options[索引] 下拉框.options.length 查找对象document.getElementsByName("r1"); document.getElementById(id); 定时timer=setInterval('scrollwindow()',delay); clearInterval(timer); UNCODE编码escape() ,unescape 父对象obj.parentElement(dhtml) obj.parentNode(dom) 交换表的行TableID.moveRow(2,1) document.all.csss.href = "a.css"; 替换CSS并排显示display:inline 隐藏焦点hidefocus=true 根据宽度换行style="word-break:break-all" 自动刷新 简单邮件 快速转到位置obj.scrollIntoView(true) 锚 anchors 网页传递参数location.search(); 可编辑obj.contenteditable=true 执行菜单命令obj.execCommand 双字节字符/[^/x00-/xff]/ 汉字/[/u4e00-/u9fa5]/ 让英文字符串超出表格宽度自动换行word-wrap: break-word; word-break: break-all; 透明背景 获得style内容obj.style.cssText HTML标签document.documentElement.innerHTML 第一个style标签document.styleSheets[0] style标签里的第一个样式document.styleSheets[0].rules[0] 防止点击空链接时，页面往往重置到页首端。word 上一网页源asp: request.servervariables("HTTP_REFERER") javascript: document.referrer 释放内存CollectGarbage(); 禁止右键document.oncontextmenu = function() { return false;} 禁止保存 禁止选取
地址栏图标href="favicon.ico"> favicon.ico 名字最好不变16*16的16色,放虚拟目录根目录下收藏栏图标 查看源码 关闭输入法 自动全选 ENTER键可以让光标移到下一个输入框 文本框的默认值 title换行obj.title = "123 sdfs " 获得时间所代表的微秒var n1 = new Date("2004-10-10".replace(/-/g, "//")).getTime() 窗口是否关闭win.closed checkbox扁平
获取选中内容document.selection.createRange().duplicate().text 自动完成功能打开该功能关闭该功能窗口最大化
创建嵌套对象24.3 删除对象中的属性24.4.1 遍历对象中的属性名1 24.4 遍历对象中的属性名24.5 obj.propertyIsEnumerable('ele') 24.6 obj.hasOwnProperty('ele') 25. toString 25.1 使用toString 列出数组中的元素26. Array() 26.0.1 简单创建数组, 并赋值2 26.0 简单创建数组, 并赋值26.0.3 创建数组中的数组26.0.4 创建数组中的对象26.0.2 简单创建数组26.1 [array].push(), [array].pop() 26.2 数组排序26.3 创建数组指定维数, 从1 开始. 27. RegExp 27.1 普通操作 1 27.2 test 语句27.3 exec 语句28. new 语法29. isNaN 30. Date() 30.1 输出年月日, 时分秒的日期格式31. function 函数31.1.1.1 三种定义函数的方法 1.1 31.10 在数组中存储函数, 并引用31.1.1 三种定义函数的方法 1 31.1.2 三种定义函数的方法2 31.1 三种定义函数的方法31.2 在标签中写函数31.3 创建嵌套函数31.4.1 创建递归函数 1 31.4 创建递归函数31.5 创建函数对象31.6 在函数内部定义的函数只能在该函数内部调用31.7 定义函数变量, 并赋值31.8 变量引用函数31.9 在对象中存储函数, 并引用31.11 function.call() 31.12 在函数内定义的变量可以被下级内嵌函数调用32. typeof 查看数据类型32.1 33. obj.valueOf() 返回原始值34. Math 对象34.1.1 生成1 至4 的随机数34.1 Math.random(); 34.2 求x 的n 次方35. delete 36. confirm() 确认框36.1 带条件确认框37. window.open 37. window 37.1 打开没有焦点的窗口38. return 返回值38.1 return true 38.2 return undefined 39. throw 39.1 简单产生错误40. arguments 40.1 判断arguments.length 40.2 列出所有argument 的值40.3 arguments.callee / 调用函数本身41. .to****** 41.1 toString 42. parseInt() / parseFolat() -------------------------------- 42. parseInt() / parseFolat() 41. .to****** 41.1 toString 40. arguments 40.1 判断arguments.length 40.2 列出所有argument 的值 40.3 arguments.callee / 调用函数本身 39. throw 39.1 简单产生错误 38. return 返回值38.1 return true 38.2 return undefined 37. window 37. window.open 37.1 打开没有焦点的窗口 36. confirm() 确认框36.1 带条件确认框 35. delete 34. Math 对象34.1 Math.random(); 34.1.1 生成1 至 4 的随机数 34.2 求x 的n 次方 33. obj.valueOf() 返回原始值 32. typeof 查看数据类型 32.1 31. function 函数31.1 三种定义函数的方法 31.1.1 三种定义函数的方法 1 31.1.1.1 三种定义函数的方法 1.1 31.1.2 三种定义函数的方法 2 31.2 在标签中写函数
创建嵌套函数 31.4 创建递归函数<% var i=0; function t(){ i++; if(i<100){ Response.Write(i+'
'); return t(); } Response.Write(i+'
'); } t(); %> 31.4.1 创建递归函数1 31.5 创建函数对象 31.6 在函数内部定义的函数只能在该函数内部调用 31.7 定义函数变量, 并赋值 31.8 变量引用函数 31.9 在对象中存储函数, 并引用 31.10 在数组中存储函数, 并引用 31.11 function.call() 31.12 在函数内定义的变量可以被下级内嵌函数调用 30. Date() 30.1 输出年月日, 时分秒的日期格式 29. isNaN 28. new 语法new Boolean(false) new Number(0) new String("") new Array() new Object() new Date(); new Error(); 27. RegExp 27.1 普通操作1 27.2 test 语句 27.3 exec 语句 26. Array() 26.0
简单创建数组, 并赋值 26.0.1 简单创建数组, 并赋值2 26.0.2 简单创建数组 26.0.3 创建数组中的数组 26.0.4 创建数组中的对象 26.1 [array].push(), [array].pop() 26.2 数组排序 26.3 创建数组指定维数, 从 1 开始. 25. toString 25.1 使用toString 列出数组中的元素 24. object 24.1 创建简单对象 24.1.1 创建简单对象一 24.1.2 创建简单对象二 24.2 创建嵌套对象 24.2.1 创建嵌套对象 1 24.3 删除对象中的属性 24.4 遍历对象中的属性名 24.4.1 遍历对象中的属性名1 24.5 obj.propertyIsEnumerable('ele') 24.6 obj.hasOwnProperty('ele') 23. call, apply 23.1 apply 23.1.1 找出数组中最大的数 22. break, continue 22.1 continue 22.2 break 22.2.1 break 标签 21. with 21.1 简单with 21.1 简单with (另一写法) var $dw=document $dw.write('ok this a test'); 20. try, catch, finally 20.1 简单try, catch try{ 5*kkk } catch(e){ alert(e) } 20.1.1 简单try, catch 1 19. for in 19.1 简单for in 19.1.1 简单for in 1 for (var $i in window){ document.write($i+'
'); } 19.2 for in 赋值[数组] var $array=new Array(); var i=0; for ($array[i++] in window){ //document.write($i+'
'); } alert($array[0]); 19.2.1 for in 赋值[数组] 1 18. for 18.1 简单for for (var $i=0; $i<10; $i++) { document.write($i) } 18.2 简单for 1 for (var $i=0, $j=10; $i<10; $i++, $j--) { document.write(($i*$j)+'
') } 18.3 循环列出从 a - z 的字母 18.3 n阶乘 18.4 Fibonacci Numbers 17. do while 17.1 简单do while var $count=0 do{ document.write($count) } while(++$count<10) 17.1.2 简单do while var $count=1 do{ document.write($count) } while($count++<10) 16. while 16. 简单while var $count=0 while($count<10){ document.write($count);$count++;} 15 if 判断15.1 简单if 判断function ubbT ag(fId, str){ document.getElementById(fId).content.focus(); var strEnd=str.replace(//[/ig,'[/') if (strEnd.indexOf('=')>-1){ strEnd=strEnd.replace(/(.*?)/=.*?/]/,'$1]') } if((document.selection)&&(document.selection.type== "Text")){ var oStr=document.selection.createRange(); oStr.text=str+oStr.text+strEnd } else { document.getElementById(fId).content.value+=str+strEnd } } 15.1.1 简单if 判断 2 15.1.2 简单if 判断 3 15.2 if 判断的三个写法 15.3 判断执行文件使用网络还是使用本地协议 15.4 if...else 写法 14. switch 14.1 简单switch /* switch(strEnd){ case '/[//html]' :strEnd=strEnd.replace(///[//,'HTML 和JS 代码支持[');break; case '/[//code]' :strEnd=strEnd.replace(///[//,'代码[');break; case '/[//quote]' :strEnd=strEnd.replace(///[//,'引用[');break; case '/[//cite]' :strEnd=strEnd.replace(///[//,'引用[');break; case '/[//linenum]' :strEnd=strEnd.replace(///[//,'显示行号[');break; case '/[//b]' :strEnd=strEnd.replace(///[//,'粗体[');break; case '/[//i]' :strEnd=strEnd.replace(///[//,'叙体[');break; case '/[//u]' :strEnd=strEnd.replace(///[//,'下划线[');break; case '/[//flash]' :strEnd=strEnd.replace(///[//,'Flash 动画[');break; case
'/[//sound]' :strEnd=strEnd.replace(///[//,'背景声音[');break; case '/[//mms]' :strEnd=strEnd.replace(///[//,'WM格式流数据[');break; case '/[//rtsp]' :strEnd=strEnd.replace(///[//,'Real格式流数据[');break; case '/[//ra]' :strEnd=strEnd.replace(///[//,'在线Real Player播放音频文件[');break; case '/[//real]' :strEnd=strEnd.replace(///[//,'Real Player 播放视频文件[');break; case '/[//wm]' :strEnd=strEnd.replace(///[//,'在线Windows Media Player播放视频文件[');break; case '/[//wma]' :strEnd=strEnd.replace(///[//,'在线Windows Media Player播放音频文件[');break; case '/[//iframe]' :strEnd=strEnd.replace(///[//,'插入网页[');break; } */ 13. 时间操作13.1 以毫秒为单位的倒计时跳转, 来源CSDN 20.000 秒后将自动跳转到12. 随机数12.1 生成GUID
*/ig document.all.textarea.value=document.all.textarea.value.replace(re,"") } 8. 顯示頁面所有元素 7. 文本框回车链接 转到: 6. IE 全屏显示 5. 双击拷贝文本 4. 控制图片大小
//如果图片宽度大于500px, 则更改宽度为500px 3.1 Javascript 结合Asp 使用数组<% '连接数据库set rs=server.CreateObject("adodb.recordset") '创建rs 数据查询rs.open "Select a.*, b.* FROM ctglossarysubcat AS a INNER JOIN ctglossarysupercat AS b ON a.gcid = b.gcid order by a.gcid",MM_conn_string,1 %> <% rs.close '关闭rs 连接set rs=nothing %> 3. 数组/Array 2.2 实时显示更改的图片链接 type="text/javascript"> //'); document.write(j); //2 document.write('
'); var k=1 l=k++ document.write(k); //2 document.write('
'); document.write(l); //1 //]]> -1.2 类型转换 -1.3 0/0=? -1.4 == 与=== -1.4.1 NaN -1.4.2 true 等价1, false 等价0. -1.5 in 操作符 -2. var 定义变量-2.1 普通定义变量 -2.1.1 普通定义变量1 -2.1.2 普通定义变量 2 -2.2 全局变量与局部变量 -2.3 在函数中使用var 定义一个变量, 该变量将影响整个函数, 不分先后. var scope = "global"; function f( ) { alert(scope); // Displays "undefined", not "global" var scope = "local"; // Variable initialized here, but defined everywhere alert(scope); // Displays "local" } f( ); -2.4 同时初始化多个变量并赋相同值 -3. 优先级-3.1 函数比其他代码优先执行 ---/--------------------------------------------------------- 常用参数3. document 2. location 1. this --------------------------------- 3.3 写出字符串document.write(""); 3.2 document.from 指定表单域3.1 document.all.id 查找指定HTML 页面ID 或名字 3. document 2.2 转到特定网页onClick="location.href=' http://127.0.0.1/'" 2.1 单独location 取页面地址 2. location 1.4 this.height 取高度属性1.3 this.width 取宽度属性 1.2 this.href 取链接地址 1.1 this.src 取图片地址 1. this
---/--------------------------------------------------------- 问题集: 3. return 返回多个值2006-10-14 14:13:18 2. 理解setInternal 用法 1. 理解void 用法---/--------------------------------------------------------- 相关摘要: 24. Keep in mind that the function statement is available in all versions of JavaScript, the Function( ) constructor is available only in JavaScript 1.1 and later, and function literals are available only in JavaScript 1.2 and later. Recall that we said the three functions defined earlier are "more or less" equivalent -- there are some differences between these three techniques for function definition, which we'll consider in Section 11.5. //JavaScript: The Definitive Guide, 4th Edition -- 7.1.3 Function Literals 2006-10-19 14:35:56 23. The Function( ) constructor expects any number of string arguments. The last argument is the body of the function -- it can contain arbitrary JavaScript statements, separated from each other by semicolons. All other arguments to the constructor are strings that specify the names of the parameters to the function being defined. If you are defining a function that takes no arguments, you simply pass a single string -- the function body -- to the constructor. //JavaScript: The Definitive Guide, 4th Edition -- 7.1.2 The Function( ) Constructor 2006-10-19 14:16:18 22. Note that ECMAScript v3 does not allow function definitions to appear anywhere; they are still restricted to top-level global code and top-level function code. This means that function definitions may not appear within loops or conditionals, for example.[1] These restrictions on function definitions apply only to function declarations with the function statement. As we'll discuss later in this chapter, function literals (another feature introduced in JavaScript 1.2 and standardized by ECMAScript v3) may appear within any JavaScript e-xpression, which means that they can appear within if and other statements. //JavaScript: The Definitive Guide, 4th Edition -- 7.1 Defining and Invoking Functions 2006-10-19 14:10:13 21. try and finally can be used together without a catch clause. In this case, the finally block is simply cleanup code that is guaranteed to be executed, regardless of any break, continue, or return statements within the try clause. For example, the following code uses a try/finally statement to ensure that a loop counter variable is incremented at the end of each iteration, even when an iteration terminates abruptly because of a continue statement: //JavaScript: The Definitive Guide, 4th Edition -- 6.17 try/catch/finally 2006-10-18 19:18:08 20. The continue statement, in both its labeled and unlabeled forms, can be used only within the body of a while, do/while, for, or for/in loop. Using it anywhere else causes a syntax error. //JavaScript: The Definitive Guide, 4th Edition -- 6.12 continue 2006-10-18 16:03:46 19. The following rules are used to determine whether two values are identical according to the === operator: If the two values have different types, they are not identical. If both values are numbers and have the same value, they are identical, unless either or both values are NaN, in which case they are not identical. The NaN value is never identical to any other value, including itself! To check whether a value is NaN, use the global isNaN( ) function. If both values are strings and contain exactly the same characters in the same positions, they are identical. If the strings differ in length or content, they are not identical. Note that in some cases, the Unicode standard allows more than one way to encode the same string. For efficiency, however, JavaScript string comparison compares strictly on a character-by-character basis, and it assumes that all strings have been converted to a "normalized form" before they are compared. See the "String.localeCompare( )" reference page in the core
reference section of this book for another way to compare strings. If both values are the boolean value true or both are the boolean value false, they are identical. If both values refer to the same object, array, or function, they are identical. If they refer to different objects (or arrays or functions) they are not identical, even if both objects have identical properties or both arrays have identical elements. If both values are null or both values are undefined, they are identical. The following rules are used to determine whether two values are equal according to the == operator: If the two values have the same type, test them for identity. If the values are identical, they are equal; if they are not identical, they are not equal. If the two values do not have the same type, they may still be equal. Use the following rules and type conversions to check for equality: If one value is null and the other is undefined, they are equal. If one value is a number and the other is a string, convert the string to a number and try the comparison again, using the converted value. If either value is true, convert it to 1 and try the comparison again. If either value is false, convert it to 0 and try the comparison again. If one value is an object and the other is a number or string, convert the object to a primitive and try the comparison again. An object is converted to a primitive value by either its toString( ) method or its valueOf( ) method. The built-in classes of core JavaScript attempt valueOf( ) conversion before toString( ) conversion, except for the Date class, which performs toString( ) conversion. Objects that are not part of core JavaScript may convert themselves to primitive values in an implementation-defined way. Any other combinations of values are not equal. As an example of testing for equality, consider the comparison: "1" == true This e-xpression evaluates to true, indicating that these very different-looking values are in fact equal. The boolean value true is first converted to the number 1, and the comparison is done again. Next, the string "1" is converted to the number 1. Since both numbers are now the same, the comparison returns true. When the equality operator in JavaScript 1.1 attempted to convert a string to a number and failed, it displayed an error message noting that the string could not be converted, instead of converting the string to NaN and returning false as the result of the comparison. This bug has been fixed in JavaScript 1.2. //JavaScript: The Definitive Guide, 4th Edition -- 5.4 Equality Operators 2006-10-16 21:56:30 18. In top-level code (i.e., JavaScript code that is not part of a function), you can use the JavaScript keyword this to refer to the global object. Within functions, this has a different use, which is described in Chapter 7. //JavaScript: The Definitive Guide, 4th Edition -- 4.6 Variables as Properties 2006-10-16 16:08:34 17. Garbage collection is automatic and is invisible to the programmer. You can create all the garbage objects you want, and the system will clean up after you! You need to know only enough about garbage collection to trust that it works; you don't have to wonder about where all the old objects go. For those who aren't satisfied, however, Section 11.3, contains further details on the JavaScript garbage-collection process. //JavaScript: The Definitive Guide, 4th Edition -- 4.5 Garbage Collection 2006-10-16 16:01:55 16. Primitive Types and Reference Types var a = [1,2,3]; // Initialize a variable to refer to an array var b = a; // Copy that reference into a new variable a[0] = 99; // Modify the array using the original reference alert(b); // Display the changed array [99,2,3] using the new reference If this result does not seem surprising to you, you're already well familiar with the distinction between primitive and reference types. If it does seem surprising, take a closer look at the second line. Note that it is the
reference to the array value, not the array itself, that is being assigned in this statement. After that second line of code, we still have only one array object; we just happen to have two references to it. //JavaScript: The Definitive Guide, 4th Edition -- 4.4 Primitive Types and Reference Types 15. 在任何情况下，如果六个月以后您还能毫不费力地阅读和理解所编写的代码，则说明这些代码写得不错。//Windows 脚本技术-- JScript -- 什么是JScript？2006-10-16 14:12:55 14. The rule that all variables declared in a function are defined throughout the function can cause surprising results. The following code illustrates this: var scope = "global"; function f( ) { alert(scope); // Displays "undefined", not "global" var scope = "local"; // Variable initialized here, but defined everywhere alert(scope); // Displays "local" } f( ); //JavaScript: The Definitive Guide, 4th Edition -- 4.3 Variable Scope 13. Variable Scope The scope of a variable is the region of your program in which it is defined. A global variable has global scope -- it is defined everywhere in your JavaScript code. On the other hand, variables declared within a function are defined only within the body of the function. They are local variables and have local scope. Function parameters also count as local variables and are defined only within the body of the function. Within the body of a function, a local variable takes precedence over a global variable with the same name. If you declare a local variable or function parameter with the same name as a global variable, you effectively hide the global variable. For example, the following code prints the word "local": var scope = "global"; // Declare a global variable function checkscope( ) { var scope = "local"; // Declare a local variable with the same name document.write(scope); // Use the local variable, not the global one } checkscope( ); // Prints "local" //JavaScript: The Definitive Guide, 4th Edition -- 4.3 Variable Scope 2006-10-16 1:11:59 12. In general, functions do not know what variables are defined in the global scope or what they are being used for. Thus, if a function uses a global variable instead of a local one, it runs the risk of changing a value upon which some other part of the program relies. Fortunately, avoiding this problem is simple: declare all variables with var //JavaScript: The Definitive Guide, 4th Edition -- 4.3 Variable Scope 2006-10-15 22:23:32 11. If you attempt to read the value of an undeclared variable, JavaScript will generate an error. If you assign a value to a variable that you have not declared with var, JavaScript will implicitly declare that variable for you. Note, however, that implicitly declared variables are always created as global variables, even if they are used within the body of a function. To prevent the creation of a global variable (or the use of an existing global variable) when you meant to create a local variable for use within a single function, you must always use the var statement within function bodies. It's best to use var for all variables, whether global or local. (The distinction between local and global variables is explored in more detail in the next section.) //JavaScript: The Definitive Guide, 4th Edition -- 4.2.1 Repeated and Omitted Declarations 2006-10-15 22:00:53 10. Error Objects ECMAScript v3 defines a number of classes that represent errors. The JavaScript interpreter "throws" an object of one of these types when a runtime error occurs. (See the throw and try statements in Chapter 6 for a discussion of throwing and catching errors.) Each error object has a message property that contains an implementation-specific error message. The types of predefined error objects are Error, EvalError, RangeError, ReferenceError, SyntaxError, TypeError, and URIError. You can find out more about these classes in the core reference section of this book. //JavaScript: The Definitive Guide, 4th
Edition -- 3.11 Error Objects 2006-10-15 19:39:08 9. undefined Another special value used occasionally by JavaScript is the undefined value returned when you use either a variable that has been declared but never had a value assigned to it, or an object property that does not exist. Note that this special undefined value is not the same as null. Although null and the undefined value are distinct, the == equality operator considers them to be equal to one another. Consider the following: my.prop == null //JavaScript: The Definitive Guide, 4th Edition -- 3.8 undefined 2006-10-15 18:02:39 8. The way to really learn a new programming language is to write programs with it. //JavaScript: The Definitive Guide, 4th Edition -- 1.10 Exploring JavaScript 2006-10-14 2:40:02 7. Both Netscape and Microsoft have made their JavaScript interpreters available to companies and programmers who want to embed them in their applications. Netscape's interpreter was released as open source and is now available through the Mozilla organization (see https://www.360docs.net/doc/4716194721.html,/js/). Mozilla actually provides two different versions of the JavaScript 1.5 interpreter. One is written in C and is called "SpiderMonkey." The other is written in Java and, in a flattering reference to this book, is called "Rhino." //JavaScript: The Definitive Guide, 4th Edition -- 1.4 JavaScript in Other Contexts 2006-10-14 1:13:44 6.
11.1.2 Explicit Type Conversions Table 11-1 listed the automatic data type conversions that JavaScript performs. It is also possible to explicitly convert values from one type to another. JavaScript does not define a cast operator as C, C++, and Java do, but it does provide similar facilities for converting data values. As of JavaScript 1.1 (and the ECMA-262 standard), Number( ) , Boolean( ), String( ), and Object( ) may be called as functions as well as being invoked as constructors. When invoked in this way, these functions attempt to convert their arguments to the appropriate type. For example, you could convert any value x to a string with String(x) and convert any value y to an object with Object(y). There are a few other tricks that can be useful for performing explicit conversions. To convert a value to a string, concatenate it with the empty string: var x_as_string = x + ""; T o force a value to a number, subtract zero from it: var x_as_number = x - 0; And to force a value to boolean, use the ! operator twice: var x_as_boolean = !!x; Because of JavaScript's tendency to automatically convert data to whatever type is required, explicit conversions are usually unnecessary. They are occasionally helpful, however, and can also be used to make your code clearer and more precise. //JavaScript: The Definitive Guide, 4th Edition -- 11.1 Data Type Conversion 2006-10-12 12:36:23 5. Each RegExp object has five properties. The source property is a read-only string that contains the text of the regular e-xpression. The global property is a read-only boolean value that specifies whether the regular e-xpression has the g flag. The ignoreCase property is a read-only boolean value that specifies whether the regular e-xpression has the i flag. The multiline property is a read-only boolean value that specifies whether the regular e-xpression has the m flag. The final property is lastIndex, a read-write integer. For patterns with the g flag, this property stores the position in the string at which the next search is to begin. It is used by the exec( ) and test( ) methods, as described in the previous section. //JavaScript: The Definitive Guide, 4th Edition -- 10.3.2 RegExp Instance Properties 2006-10-9 21:23:26 4. the RegExp constructor. search( ) does not support global searches -- it ignores the g flag of its regular e-xpression argument. //JavaScript: The Definitive Guide, 4th Edition -- 10.2 String Methods for Pattern Matching 2006-10-9
19:56:40 3. We've seen the . operator used to access the properties of an object. It is also possible to use the [] operator, which is more commonly used with arrays, to access these properties. Thus, the following two JavaScript e-xpressions have the same value: object.property object["property"] //JavaScript: The Definitive Guide, 4th Edition -- 8.6 Objects as Associative Arrays 2006-10-9 14:45:13 2. The typeof Operator typeof is a unary operator that is placed before its single operand, which can be of any type. Its value is a string indicating the data type of the operand. The typeof operator evaluates to "number", "string", or "boolean" if its operand is a number, string, or boolean value. It evaluates to "object" for objects, arrays, and (surprisingly) null. It evaluates to "function" for function operands and to "undefined" if the operand is undefined. //JavaScript: The Definitive Guide, 4th Edition -- 5.10.2 The typeof Operator 1. JavaScript strings (and JavaScript arrays, as we'll see later) are indexed starting with zero. ---/--------------------------------------------------------- 小小心得1. 花括弧定义对象元素, 方括弧定义数组元素. 2006-10-15 17:55:50 2. Javascript 正则表达式摘要linenum Javascript 与正则表达式By shawl.qiu 语法方法: 5. str.split() 4. str.match() 3. str.replace() 2. str.search() 1. 子匹配 0. 创建正则表达式模式0.1 new RegExp() -1. re.exec(str) -2. re.test(str) ---/---------------------------------------- 摘要: 4. The String methods search( ) , replace( ), and match( ) do not use the lastIndex property as exec( ) and test( ) do. In fact, the String methods simply reset lastIndex( ) to 0. If you use exec( ) or test( ) on a pattern that has the g flag set and you are searching multiple strings, you must either find all the matches in each string, so that lastIndex is automatically reset to zero (this happens when the last search fails), or you must explicitly set the lastIndex property to 0 yourself. If you forget to do this, you may start searching a new string at some arbitrary position within the string rather than from the beginning. Finally, remember that this special lastIndex behavior occurs only for regular e-xpressions with the g flag. exec( ) and test( ) ignore the lastIndex
property of RegExp objects that do not have the g flag. //JavaScript: The Definitive Guide, 4th Edition -- 10.3.1 RegExp Methods for Pattern Matching 2006-10-20 18:10:36 3. match method The match( ) method is the most general of the String regular e-xpression methods. It takes a regular e-xpression as its only argument (or converts its argument to a regular e-xpression by passing it to the RegExp( ) constructor) and returns an array that contains the results of the match. If the regular e-xpression has the g flag set, the method returns an array of all matches that appear in the string. For example: "1 plus 2 equals 3".match(//d+/g) // returns ["1", "2", "3"] //JavaScript: The Definitive Guide, 4th Edition -- 10.2 String Methods for Pattern Matching 2006-10-20 17:23:08 2. search method Strings support four methods that make use of regular e-xpressions. The simplest is search( ). This method takes a regular e-xpression argument and returns either the character position of the start of the first matching substring, or -1 if there is no match. For example, the following call returns 4: "JavaScript".search(/script/i); If the argument to search( ) is not a regular e-xpression, it is first converted to one by passing it to the RegExp constructor. search( ) does not support global searches -- it ignores the g flag of its regular e-xpression argument. //JavaScript: The Definitive Guide, 4th Edition -- 10.2 String Methods for Pattern Matching 1. A number of punctuation characters have special meanings in regular e-xpressions. They are: ^ $ . * + ? = ! : | / / ( ) [ ] { } //JavaScript: The Definitive Guide, 4th Edition -- 10.1 Defining Regular Expressions