事件处理程序调用错误的上下文

Question

在SomeObj对象中，onkeydown事件处理程序this.doSomething在错误的上下文（textbox元素的上下文）中调用，但需要在this的上下文中调用它。怎么办呢？

function SomeObj(elem1, elem2) {
    this.textboxElem = elem1;
    this.someElem = elem2;
    this.registerEvent();
}

SomeObj.prototype = {
    registerEvent: function() {
        this.textboxElem.onkeydown = this.doSomething;
    },
    doSomething: function() {
        // this must not be textboxElem
        alert(this);
        this.someElem.innerHTML = "123";
    }
};

Answer 1

将引用复制到局部变量，以便在闭包中使用它：

registerEvent: function() {
  var t = this;
  this.textboxElem.onkeydown = function() {
    t.doSomething();
  };
},