javascript function 初探

1、The JavaScript函數(shù)Function Part11Content基本原理作用域scope閉包closure21.1 這是函數(shù)嗎？function(a,b) return a+b;31.2 函數(shù)是在定義時：函數(shù)名稱函數(shù)的預(yù)期參數(shù)函數(shù)體函數(shù)的作用域41.3 函數(shù)還是在執(zhí)行時參數(shù)對象callerthis51.2.1 函數(shù)名稱(function() alert()()var car = function()alert()function bingo()alert()var car = f

2、unction acar()alert()6 1.2.2 函數(shù)的預(yù)期參數(shù)function add(a,b) console.log(arguments.callee.length) /2console.log(add.length) /2add(1,2,3)function.length71.2 函數(shù)是在定義時：函數(shù)名稱函數(shù)的預(yù)期參數(shù)函數(shù)體函數(shù)的作用域8 1.3.1 參數(shù)對象argumentsfunction add(a,b) console.log(arguments.length) /3 console.log(arguments0) /1 console.log(argu

3、ments.callee = add) /trueconsole.log(add.length) /2add(1,2,3)9 1.3.2 callerfunction.callerfunction x(value) console.log(x.caller)function caller()x.call();var anotherCaller=function()x(); x();caller();anotherCaller();nullfunction caller() x.call(); function () x(); 101.3 函數(shù)還是在執(zhí)行時參數(shù)對象callerthis112.1作

4、用域符號被定義的區(qū)間包括局部變量，全局變量，函數(shù)參數(shù)和閉包變量總之，不用this就可以訪問的變量都是作用域中的變量作用域是鏈?zhǔn)降膙ar name = dog ,function callName(name)var name = cat alert(name)callName( bird ) / cat122.2作用域定義function mine(a,b)if(ab) var t=b-a return tmine(2,5) / 3c：函數(shù)開始c+：函數(shù)，塊，類，命名空間java：函數(shù)，塊js：函數(shù)內(nèi)部var name = dogfunction callName(name) alert(nam

5、e) var name = cat alert(name) callName()132.3作用域查找function factory() var name = dog;var intro = function()alert(I am + name);return intro;function app()var name = cat;var func = factory();func();app();argumentsargumentsname:dogintro:functionfactory:functionapp:function142.3作用域查找“JS中的函數(shù)運(yùn)行在它們被定義的作用域里,

6、而不是它們被執(zhí)行的作用域里.”JS權(quán)威指南153.1閉包 closurefunction x( value ) return function() return value;var fooa = x(5);var foob = x(8);console.log(fooa();console.log(foob();/output/5855 ?58 ?88 ?163.2閉包 定義如果某個作用域內(nèi)部有其他的作用域，則該作用域會被保留(即便該作用域內(nèi)部的代碼已經(jīng)執(zhí)行完成)，直到內(nèi)部的函數(shù)也被釋放173.3閉包的作用function x( value ) return function() return

7、 value;type = “dog”var intro=function()var sound=“”if(type = “dog”) sound=“wa.wanf”;else if(type = “cat”) sound=“miao.”;intro = x(sound);return xtype = “dog”var intro=function()var sound=“”if(type = “dog”) sound=“wa.wanf”;else if(type = “cat”) sound=“miao.”;return x183.4閉包的危害function()var a,b,c,d,e,f,g;var dom/do stuffdom.onclick=function(e)console.log(e.target)function()var a,b,c,d,e,f,g;var dom/do stuffdom.onclick=domClick;function domC