Event Handler Called With Wrong Context

问题

In the SomeObj object, the onkeydown event handler this.doSomething is called in the wrong context (that of the textbox element) but it needs to be called in the context of this. How can this be done?

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";
    }
};

回答1:

Copy the reference to a local variable, so that you can use it in a closure:

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

来源：https://stackoverflow.com/questions/6300817/event-handler-called-with-wrong-context