为什么这段代码不能像下面的代码那样工作，但是如果我注释掉 function testBgChange(){函数并将代码保留在该函数中，它将可以正常工作.如果我将代码保留在函数中，然后调用该函数，会有什么区别?
How come this code does not work as its written below but if I comment out function testBgChange(){ and keep the code inside that function it works fine. What difference does it make if I keep the code within the function and then call that function?
<html> <head> <script type="text/javascript"> testBgChange(); function testBgChange(){ var i = 0; var c = 0; var time = 3000; var incr = 3000; while(i<=3){ if(c==0){ var red = "#FF0000"; setTimeout("changeBgColor(red)",time); time+=incr; c=1; } else if(c==1){ var white = "#FFFFFF"; setTimeout("changeBgColor(white)",time); time+=incr; c=0; } i+=1; } } function changeBgColor(color){ document.getElementById("alert").style.backgroundColor = color; } </script> </head> <body> <p id="alert"> <br> <br> Testing <br> <br> </p> </body> </html> 推荐答案由于在函数中声明 var red 和 var white 时，只能从内部访问功能.这是一个问题，因为 setTimeout 将在全局范围内调用 eval ，而该全局范围无法访问这些变量.
Because var red and var white, when declared inside the function, can only be accessed from within the function. This is a problem becausesetTimeout will call eval in the global scope, which does not have access to these variables.
有多种方法可以解决此问题，但是最好给 setTimeout 一个函数而不是字符串.当新函数创建一个 closure 并保留对包含函数中变量的访问权限时，这将解决您的问题:
There are a variety of ways to work around this, but it's better practice to give setTimeout a function rather than a string. This will solve your problem as the new function creates a closure that retains access to the variables in the containing function:
var red = "#FF00000"; setTimeout(function () { changeBgColor(red); }, time);更多推荐
仅在函数外部起作用的javascript代码
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