once

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2023-12-01

描述 (Description)

它就像一个on事件，但导致绑定回调只在被删除之前触发一次。

语法 (Syntax)

object.once(event, callback function, [context])

参数 (Parameters)

event - 它绑定一个对象。
callback - 它是对代码的引用。
context - 它是一个可以传递给回调函数的对象。

例子 (Example)

<!DOCTYPE html>
<html>
   <head>
      <title>Event Once Example</title>
      <script src = "https://code.jquery.com/jquery-2.1.3.min.js"
         type = "text/javascript"></script>
      <script src = "https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.8.2/underscore-min.js"
         type = "text/javascript"></script>
      <script src = "https://cdnjs.cloudflare.com/ajax/libs/backbone.js/1.1.2/backbone-min.js"
         type = "text/javascript"></script>
   </head>
   <body>
      <script type = "text/javascript">
         //The created object 'myVal' is extended using Backbone.Events method
         var myVal = _.extend({name:'xnip!!!'}, Backbone.Events);
         //The once() method causes the bound callback to only fire once before being removed
         myVal.once('hello', function () {
            document.write("The value after firing once is: ");
            document.write(this.name);//name will get displayed by referring the current object
         });
         //It triggers the 'hello' event on object 'myVal'
         myVal.trigger('hello');
      </script>
   </body>
</html>