javascript 将范围传递给 forEach
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Passing scope to forEach
提问by leemour
I'm trying to use a callback method addToCountinstead of anonymous function in forEach. But I can't access this.countin it (returns undefined).
我正在尝试使用回调方法addToCount而不是forEach. 但我无法访问this.count它（返回undefined）。
function Words(sentence) {
this.sentence = sentence;
this.count = {};
this.countWords();
}
Words.prototype = {
countWords: function() {
var words = this.sentence.split(/\W+/);
words.forEach(this.addToCount);
},
addToCount: function(word) {
word = word.toLowerCase();
if (word == '') return;
if (word in this.count)
this.count[word] += 1;
else
this.count[word] = 1;
}
}
I think the problem is the scope. How can I pass thisto addToCountor is there any other way to make it work?
我认为问题在于范围。我如何传递this给addToCount或有其他方法可以使其工作？
回答by lonesomeday
You need to use Function#bindto bind a scope:
您需要使用Function#bind来绑定范围：
words.forEach(this.addToCount.bind(this));
Note that this is not available in all browsers: you should use a shim (as provided in the link above) to add it in the browsers that don't support Function#bind.
请注意，这并非在所有浏览器中都可用：您应该使用 shim（如上面的链接中提供的）将其添加到不支持Function#bind.
As dandavis points out in the comments, you can pass a value to Array#forEachas the context for the callback:
正如 dandavis 在评论中指出的，您可以传递一个值Array#forEach作为回调的上下文：
words.forEach(this.addToCount, this);
回答by NickM
Try something like this. I've used thatrather than _thisbut also I've moved addToCountso it's inside countWords. That turns countWordsinto a closure containing that.
尝试这样的事情。我使用了that而不是，_this但我也移动了addToCount所以它在里面countWords。这变成countWords了一个包含它的闭包。
Words.prototype = {
countWords: function() {
var that = this, words = this.sentence.split(/\W+/);
words.forEach(function(word) {
word = word.toLowerCase();
if (word == '') return;
if (word in that.count)
that.count[word] += 1;
else
that.count[word] = 1;
});
}
}
