javascript - Nodejs 从函数内部调用函数

Question

我有3种方法

exports.getImageById = function (resultFn, id) {
 ...
}

exports.getCollectionById = function (resultFn, id) {
}

在第三个方法中我想调用这两个方法

exports.getCollectionImages = function (resultFn, collectionId) {

var arr = new Array();

this.getCollectionById(   // fine, 1st call
    function (result) {
        var images = result.image;
        for (i = 0; i < images.length; i++) {
            this.getImageById(function (result1) {   // error, 2nd call
                    arr[i] = result1;
                }, images[i]
            );

         }
    }
    , collectionId
);

resultFn(arr);
}

我可以调用第一个函数this.getCollectionById，但它无法调用this.getImageById，它说未定义函数，是什么原因？

Answer 1

当您调用 this.getCollectionById 并向其传递回调时，回调无法访问相同的 this

最简单的解决方案是将 this 保存为局部变量。

exports.getCollectionImages = function (resultFn, collectionId) {    
    var arr = new Array();        
    var me = this; // Save this
    this.getCollectionById(   // fine, 1st call
        function (result) {
            var images = result.image;
            for (var i = 0; i < images.length; i++) {
                // Use me instead of this
                me.getImageById(function (result1) {   // error, 2nd call
                    arr[i] = result1;
                }, images[i]);
            }
        }, collectionId);
    resultFn(arr);
}