我如何获得正确的"this"?在Array.map中? [英] How do I get the right "this" in an Array.map?

问题描述

我假设这里有call或apply的某些应用程序，但是我不确定如何实现它.

I assume there is some application of call or apply here but I'm not sure how to implement it.

http://codepen.io/anon/pen/oXmmzo

a = {
  foo: 'bar',
  things: [1, 2, 3],
  showFooForEach: function() {
    this.things.map(function(thing) {
      console.log(this.foo, thing);
    });
  }
}

a.showFooForEach();

说我想map一个数组，但是在函数中，我需要访问foo所属的this. map的function创建了一个新的this上下文，因此我显然需要以某种方式强制返回该上下文，但是在仍然可以访问thing的情况下该如何做呢?

Say I want to map an array, but in the function, I need access to the this to which foo belongs. The function of map creates a new this context, so I obviously need to coerse that context back in somehow, but how do I do that while still having access to thing?

推荐答案

我意识到我应该更仔细地阅读Array.map()的文档.只需将this值作为map()

Just realized I should have read the documentation for Array.map() more carefully. One simply needs to pass in the this value as the second parameter of map()

http://codepen.io/anon/pen/VLggpX

a = {
  foo: 'bar',
  things: [1, 2, 3],
  showFooForEach: function() {
    this.things.map(function(thing) {
      console.log(this.foo, thing);
    }, this);
  }
}
a.showFooForEach();

此外，对于认真的JavaScript开发人员来说，必须了解bind()，call()和apply()的工作方式.这些使我们可以跳过诸如此类的愚蠢任务

In addition, understanding how bind(), call() and apply() work are a must for serious JavaScript developers. These allow us to skip silly assignments like

var self = this;
myItems.map(function(item) {
  self.itemArray.push(item);
});

使用

myItems.map(function(item) {
  this.itemArray.push(item);
}.bind(this));

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