带有和不带引号和括号的setTimeout之间的区别 [英] Difference between setTimeout with and without quotes and parentheses
问题描述
我正在学习JavaScript，最近我学到了关于JavaScript计时事件的知识。当我在 W3Schools setTimeout 时>，我注意到一个奇怪的人物，我之前没有遇到过。他们使用双引号然后调用函数。
I am learning JavaScript and I have learned recently about JavaScript timing events. When I learned about setTimeout at W3Schools, I noticed a strange figure which I didn’t run into before. They are using double quotes and then call the function.
示例：
setTimeout("alertMsg()", 3000);
我知道JavaScript中的双引号和单引号表示字符串。
I know that double and single quotes in JavaScript means a string.
我也看到我可以这样做：
Also I saw that I can do the same like that:
setTimeout(alertMsg, 3000);
使用它所引用的括号，没有括号将其复制。当我使用引号和括号时，它变得疯狂。
With the parentheses it’s referring, without the parentheses it’s copied. When I am using the quotes and the parentheses it’s getting crazy.
如果有人能向我解释这三种使用方法之间的差异，我会很高兴 setTimeout ：
I will be glad if someone can explain to me the difference between these three ways of using setTimeout:
括号：
setTimeout("alertMsg()", 3000);
没有引号和括号：
setTimeout(alertMsg, 3000);
第三种只使用报价：
setTimeout("alertMsg", 3000);
注意：<$ c $的更好来源c> setTimeout 引用将是 MDN 。
推荐答案
使用 setInterval 或 setTimeout
您应该将对函数的引用作为 setTimeout 的第一个参数传递给的setInterval 。此引用可以采用以下形式：
Using setInterval or setTimeout
You should pass a reference to a function as the first argument for setTimeout or setInterval. This reference may be in the form of:
-
匿名函数
An anonymous function
setTimeout(function(){/* Look mah! No name! */},2000);
现有功能的名称
A name of an existing function
function foo(){...}
setTimeout(foo, 2000);
指向现有函数的变量
A variable that points to an existing function
var foo = function(){...};
setTimeout(foo, 2000);
请注意我将函数中的变量与函数名称分开设置。变量和函数名称占用相同的命名空间并且可以互相破坏是不明显的。
要调用函数并传递参数，可以在分配给计时器的回调中调用函数：
To call a function and pass parameters, you can call the function inside the callback assigned to the timer:
setTimeout(function(){
foo(arg1, arg2, ...argN);
}, 1000);
还有另一种方法可以将参数传递给处理程序，但它不兼容跨浏览器。
There is another method to pass in arguments into the handler, however it's not cross-browser compatible.
setTimeout(foo, 2000, arg1, arg2, ...argN);
回调上下文
默认情况下，执行时回调的上下文（计数器调用的函数内的 this 的值）是全局对象窗口 。如果您想更改它，请使用 bind 。
Callback context
By default, the context of the callback (the value of this inside the function called by the timer) when executed is the global object window. Should you want to change it, use bind.
setTimeout(function(){
this === YOUR_CONTEXT; // true
}.bind(YOUR_CONTEXT), 2000);
安全性
虽然有可能，但是你应不将字符串传递给 setTimeout 或 setInterval 。传递字符串使 setTimeout（）或 setInterval（）使用类似于 eval（） 执行字符串作为脚本，任意可能有害的脚本执行。
Security
Although it's possible, you should not pass a string to setTimeout or setInterval. Passing a string makes setTimeout() or setInterval() use a functionality similar to eval() that executes strings as scripts, making arbitrary and potentially harmful script execution possible.
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