Javascript setInterval和`this`解决方案

Question

我需要this从setInterval处理程序访问

prefs: null,
startup : function()
    {
        // init prefs
        ...
        this.retrieve_rate();
        this.intervalID = setInterval(this.retrieve_rate, this.INTERVAL);
    },

retrieve_rate : function()
    {
        var ajax = null;
        ajax = new XMLHttpRequest();
        ajax.open('GET', 'http://xyz.com', true);
        ajax.onload = function()
        {
            // access prefs here
        }
    }

如何在中访问this.prefs ajax.onload？

Answer 1

setInterval行应如下所示：

 this.intervalID = setInterval(
     (function(self) {         //Self-executing func which takes 'this' as self
         return function() {   //Return a function in the context of 'self'
             self.retrieve_rate(); //Thing you wanted to run as non-window 'this'
         }
     })(this),
     this.INTERVAL     //normal interval, 'this' scope not impacted here.
 );

编辑 ：相同的原则适用于“
onload”。在这种情况下，“外部”代码几乎不做任何事情，它只是建立一个请求，然后发送它。在这种情况下，不需要上面代码中的额外功能。您的retrieve_rate应该看起来像这样：-

retrieve_rate : function()
{
    var self = this;
    var ajax = new XMLHttpRequest();
    ajax.open('GET', 'http://xyz.com', true);
    ajax.onreadystatechanged= function()
    {
        if (ajax.readyState == 4 && ajax.status == 200)
        {
            // prefs available as self.prefs
        }
    }
    ajax.send(null);
}