一个类中的Javascript递归

Question

我试图让一个递归方法在类上下文中工作.在我的课堂上,我有以下方法:

    countChildren(n, levelWidth, level) {
    if (n.children && n.children.length > 0) {
        if (levelWidth.length <= level + 1) {
            levelWidth.push(0);
        }
        levelWidth[level + 1] += n.children.length;
        n.children.forEach(function (n) {
            this.countChildren(n, levelWidth, level+1);
        });    
    }
    // Return largest openend width
    return levelWidth;
}

但是,当我使用这个方法(之前我刚刚使用它时工作function countChildren = ...)时,它不能......找到(？)本身:Cannot read property 'countChildren' of undefined在递归时.

有没有人有任何想法？

Answer 1

尝试在构造函数中绑定方法.
此外,通过使用箭头函数,您forEach可以保持类的范围this.

export class MyClass {
    constructor(){
        this.countChildren = this.countChildren.bind(this);
    }

    countChildren(n, levelWidth, level){ ... }


    countChildren(n, levelWidth, level) {
        if (n.children && n.children.length > 0) {
            if (levelWidth.length <= level + 1) {
                levelWidth.push(0);
            }
            levelWidth[level + 1] += n.children.length;
            n.children.forEach( n => { // arrow function do not need to rebind this
                this.countChildren(n, levelWidth, level+1);
            });    
        }
        // Return largest openend width
        return levelWidth;
    }
}

Answer 2

问题出现了,因为在你的循环中,this重新定义到内部函数范围.

countChildren(n, levelWidth, level) {
    var self = this; // Get a reference to your object.

    if (n.children && n.children.length > 0) {
        if (levelWidth.length <= level + 1) {
            levelWidth.push(0);
        }
        levelWidth[level + 1] += n.children.length;

        n.children.forEach(function (n) {
            // Use "self" instead of "this" to avoid the change in scope.
            self.countChildren(n, levelWidth, level+1);
        });    
    }
    // Return largest openend width
    return levelWidth;
}