Javascript "apply" 函数似乎不适用于全局 "this"？

Question

我在nodejs中测试了'this'关键字的范围：

color = 'red';
var o = {
    color: 'blue'
};

function say() {
    console.log(this.color);
};
say.apply(this);  //'undefined'
say.apply(global);//'red'

在浏览器中：

color = 'red';
var o = {
    color: 'blue'
};

function say() {
    alert(this.color);
};
say.apply(this);  //'undefined'
say.apply(window);//'red'

var color = 'red';
function say() {
  alert(this.color);
}
say.apply(this);   //'red'
say.apply(window); //'red'

结果对我来说有点奇怪：只要"this"是指向"global"或"window"的指针，为什么say.apply(this)会输出'undefined'?

谢谢。

Answer 1

在这种情况下，您的 this 确实不够精细，因为 color = 'red'; 具有以下等价物：global.color = 'red';。要使其与 this 相关联，您需要自己完成：this.color = 'red';

要从 o 对象中获取颜色值，您需要这样写：

say.apply(o);

这是使用 apply():

的好例子

function printArgs() {
  var join = [].join; // copy link of array.join into variable

  // call join with "this=arguments",
  // this call is equivalent with "arguments.join(':')"
  // here we have guarantee that method 'join()' was called from 'arguments'
  // (not from other object)
  var argStr = join.apply(arguments, [':']);

  console.log( argStr ); // output will looks like '1:2:3'
}

printArgs(1, 2, 3);

您还可以在这里找到有用的信息：

Meaning of "this" in node.js modules and functions
What is the difference between call and apply?
Javascript call() & apply() vs bind()?

Javascript "apply" 函数似乎不适用于全局 "this"？

Javascript "apply" function seems not working for global "this"?

javascript

scope

global

window

this