在 JavaScript 中使用参数调用 apply 方法
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Call apply method with arguments in JavaScript
提问by dkugappi
I wanted to invoke a function using the javascript apply() method. This works fine if the function has no arguments. i.e.
我想使用 javascript apply() 方法调用一个函数。如果函数没有参数，这可以正常工作。IE
function test()
{
console.log(this);
}
body = document.getElementsByTagName("body")[0]; // shortcut to body element
test.apply(body); // returns [object HTMLBodyElement]
But I can't seem to do the same thing to invoke a function that has arguments:
但我似乎不能做同样的事情来调用一个有参数的函数：
function test(msg)
{
console.log(msg);
}
body = document.getElementsByTagName("body")[0]; // shortcut to body element
test(this).apply(body); // mysteriously returns the correct result, then
// typeError: 'undefined' is not an object (evaluating "test(this).apply".
The examples above are completely trivial but the grain of my question is: How do I use the apply() method to invoke a function with arguments.
上面的例子完全是微不足道的，但我的问题的核心是：如何使用 apply() 方法来调用带参数的函数。
回答by John Keyes
applytakes two arguments:
apply需要两个参数：
test.apply(null, [body]);
The first argument sets the value of thiswhen the function is executed. The second is an array of parameters for that function.
第一个参数设置this函数执行时的值。第二个是该函数的参数数组。
In your examples you could rewrite it as follows:
在您的示例中，您可以将其重写如下：
function test() {
console.log(this);
}
and call it as follows:
并按如下方式调用它：
test.apply(this);
回答by CMS
First notice that you are actually invoking your function immediately, the line:
首先请注意，您实际上是在立即调用您的函数，该行：
test(this).apply(body);
Fails because at first, you call the testfunction passing thisas an argument, and then you try to access an applyproperty on the function's result, which is undefinedsince your function doesn't return anything.
失败，因为首先，您调用作为参数test传递this的函数，然后您尝试访问apply函数结果的属性，这是undefined因为您的函数不返回任何内容。
That property access on the undefinedvalue is giving you the TypeErrorexception.
对该undefined值的属性访问为您提供了TypeError例外。
Now, let's see what you actually want to do, if you want to pass the value of the bodyvariable as the argument of your function, setting the outer thisvalue, as the thisvalue of test, you can do:
现在，让我们看看您真正想要做什么，如果您想将body变量的值作为函数的参数传递，将外部this值设置为 的this值test，您可以执行以下操作：
test.apply(this, [body]);
But that's why the callmethod exists, when you know exactly which arguments to pass, you don't need to create an array for nothing, you just pass the arguments:
但这就是该call方法存在的原因，当您确切地知道要传递哪些参数时，您无需无缘无故地创建数组，只需传递参数即可：
test.call(this, body);
The applymethod is really useful when you deal with for example a dynamic number of arguments, when you know which arguments want to pass, and still have the ability of setting the thisvalue, callis just what you need.
apply当您处理例如动态数量的参数时，该方法非常有用，当您知道要传递哪些参数并且仍然具有设置this值的能力时，call这正是您所需要的。
回答by bittersweetryan
With apply you send an array of arguments as its second argument:
使用 apply 你发送一个参数数组作为它的第二个参数：
test.apply(body,["Hello World"]);
Here is the apply documentation on the MDN docs https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Function/apply
这是 MDN 文档上的应用文档https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Function/apply
回答by bbg
Be sure to add in the argument:
请务必在参数中添加：
test.apply(body, ["my message here"]);
