javascript - 内部函数变量丢失外部函数的 'this' 值

Question

我在 JavaScript 中创建了一个类，如下所示:

class TreeMatching
{
        constructor()
        {
            this.thresholdPoints=0;
            this.neighborWeight = 0.4;
            this.totalFrequency = 0.0;
            this.listSeq = [];
            this.listFreq = [];
            this.mapScore = new Object();
            this.tree = new Trie();
        }

        createTree()
        {
            var list_Dictionary;
            var loadWordList = $.get("../wordFrequencyTop5000.txt", function(data)
            {
                list_Dictionary = data.split("\n");
            });

            loadWordList.done(function()
            {
                for(var i=0;i<list_Dictionary.length;i++)
                {
                    var string = list_Dictionary[i];
                     this.tree.insert(string); //<-- Cannot read property 'insert' of undefined
                }
            });

       }
}

它应该调用 Trie 类中的 insert 方法，如下所示:

class Trie
{
        constructor()
        {
            this.count=1;
            this.root = new TrieNode();
        }

        insert(word)
        {
            var children = new Object();

            for(var i=0; i<word.length(); i++){
                var c = word.charAt(i);

                var t;
                if(children[c]){
                        t = children[c];
                }else{
                    t = new TrieNode(c);
                    children.put(c, t);
                }

                children = t.children;

                //set leaf node
                if(i==word.length()-1)
                    t.isLeaf = true;   
            }
        }
}

但是，标记错误的代码行，即外部函数的 this 值，没有属性 tree、mapScore 等。

有没有办法可以从内部回调函数访问这些值？

谢谢

Answer 1

look at 'this' - 您必须定义局部变量以在调用内维护对“this”的引用，如链接中所述。

createTree()
        { 
            var self = this;
            var list_Dictionary;
            var loadWordList = $.get("../wordFrequencyTop5000.txt", function(data)
            {
                list_Dictionary = data.split("\n");
            });

            loadWordList.done(function()
            {
                for(var i=0;i<list_Dictionary.length;i++)
                {
                    var string = list_Dictionary[i];
                     self.tree.insert(string); //<-- Now you should be able to do it
                }
            });

       }