这个获取呼叫问题

Question

我在骨干视图中有以下代码:

var BookView = Backbone.View.extend({

initialize: function() {
    this.render();
},

render: function() {

  this.model.fetch({
    success : function(model, resp, opt) {
       alert(this.$el.html() ); //THIS ONE DOESN'T WORK?
    }
  });
  alert(this.$el.html() ); // THIS ONE WORKS FINE
}

});

我有两个alert(this.$el.html() );电话,一个在提取之外,一个在里面.但由于某种原因,fetch调用之外的那个工作,但fetch调用内的一个返回错误: Uncaught TypeError: Cannot read property 'html' of undefined

Answer 1

在里面success,this不再是View(它是undefined在严格的模式,或window其他).

要解决这个问题,你可以使用常用的var that = this习语; 有关这个成语的更多信息,请参阅:'var that = this;' 用JavaScript表示？

var BookView = Backbone.View.extend({

initialize: function() {
    this.render();
},

render: function() {
  var that = this; // define here

  this.model.fetch({
    success : function(model, resp, opt) {
       alert(that.$el.html() ); // Use that instead of this here.
    }
  });
  alert(this.$el.html() ); // THIS ONE WORKS FINE
}

});

替代选项:请参阅.bind() - 一个体面的求助:https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/bind

render: function() {
  this.model.fetch({
    success : function(model, resp, opt) {
       alert(that.$el.html() ); 
    }.bind(this) // this.model.fetch.success now has bound 'this' permanently for any call to success from this method form here on out. 
  });
  alert(this.$el.html() );
}