javascript - Javascript从窗口对象访问类变量

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How to access the correct `this` inside a callback?
                                
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                                5年前关闭。
            
                    
我想知道是否可以从以下代码中的window.updateFoo（）访问foo：

function f1 () {
    'use strict';
    this.x = {};
    this.x.foo = 0;

    window.updateFoo = function(val){
       this.x.foo = val;       // Obviously wrong since 'this' doesn't refer to f1 now. Uncaught TypeError: Cannot set property 'foo' of undefined
    };
    window.updateFoo(20);      // Try changing the value of this.x.foo?
}

最佳答案

调用window.updateFoo时，将在window的上下文中调用它。最好的选择是将this保存在变量中，然后在函数中使用它：

function f1 () {
    'use strict';
    this.x = {};                // Object for 'const' variables
    this.x.foo = 0;

    var _this = this;

    window.updateFoo = function(val){
       _this.x.foo = val;       // Use saved version
    };
    window.updateFoo(20);      // Try changing the value of this.x.foo?
}

另一个选项（但仅在f1中有效）是在特定上下文中调用updateFoo：

window.updateFoo.call(this, 20);