jQuery.proxy()

jQuery

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jQuery.proxy()

Categories: Events > Event Handler Attachment | Utilities

jQuery.proxy( function, context ) Returns: Function

Description: Takes a function and returns a new one that will always have a particular context.

  • version added: 1.4jQuery.proxy( function, context )

    • function
      Type: Function()
      The function whose context will be changed.
    • context
      Type: PlainObject
      The object to which the context (this) of the function should be set.

  • version added: 1.4jQuery.proxy( context, name )

    • context
      Type: PlainObject
      The object to which the context of the function should be set.
    • name
      Type: String
      The name of the function whose context will be changed (should be a property of the context object).

  • version added: 1.6jQuery.proxy( function, context [, additionalArguments ] )

    • function
      Type: Function()
      The function whose context will be changed.
    • context
      Type: PlainObject
      The object to which the context (this) of the function should be set.
    • additionalArguments
      Type: Anything
      Any number of arguments to be passed to the function referenced in the function argument.

  • version added: 1.6jQuery.proxy( context, name [, additionalArguments ] )

    • context
      Type: PlainObject
      The object to which the context of the function should be set.
    • name
      Type: String
      The name of the function whose context will be changed (should be a property of the context object).
    • additionalArguments
      Type: Anything
      Any number of arguments to be passed to the function named in the name argument.

This method is most useful for attaching event handlers to an element where the context is pointing back to a different object. Additionally, jQuery makes sure that even if you bind the function returned from jQuery.proxy() it will still unbind the correct function if passed the original.

Be aware, however, that jQuery's event binding subsystem assigns a unique id to each event handling function in order to track it when it is used to specify the function to be unbound. The function represented by jQuery.proxy() is seen as a single function by the event subsystem, even when it is used to bind different contexts. To avoid unbinding the wrong handler, use a unique event namespace for binding and unbinding (e.g., "click.myproxy1") rather than specifying the proxied function during unbinding.

As of jQuery 1.6, any number of additional arguments may supplied to $.proxy(), and they will be passed to the function whose context will be changed.

Examples:

Example: Change the context of functions bound to a click handler using the "function, context" signature. Unbind the first handler after first click.

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                                        <!DOCTYPE html>
                                      
                                    

                                  

                                  

                                    

                                      
                                        <html>
                                      
                                    

                                  

                                  

                                    

                                      
                                        <head>
                                      
                                    

                                  

                                  

                                    

                                        <script src="http://code.jquery.com/jquery-latest.js"></script>
                                    

                                  

                                  

                                    

                                      
                                        </head>
                                      
                                    

                                  

                                  

                                    

                                      
                                        <body>
                                      
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                      <p><button type="button" id="test">Test</button></p>
                                    

                                  

                                  

                                    

                                      
                                        <div id="log">
                                        </div>
                                      
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                      
                                        <script>
                                        
                                      
                                    

                                  

                                  

                                    

                                      var me = {
                                    

                                  

                                  

                                    

                                        type: "zombie",
                                    

                                  

                                  

                                    

                                        test: function(event) {
                                    

                                  

                                  

                                    

                                          /* Without proxy, `this` would refer to the event target */
                                    

                                  

                                  

                                    

                                          /* use event.target to reference that element. */
                                    

                                  

                                  

                                    

                                          var element = event.target;
                                    

                                  

                                  

                                    

                                          $(element).css("background-color", "red");
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                          /* With proxy, `this` refers to the me object encapsulating */
                                    

                                  

                                  

                                    

                                          /* this function. */
                                    

                                  

                                  

                                    

                                          $("#log").append( "Hello " + this.type + "<br>" );
                                    

                                  

                                  

                                    

                                          $("#test").off("click", this.test);
                                    

                                  

                                  

                                    

                                        }
                                    

                                  

                                  

                                    

                                      };
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                      var you = {
                                    

                                  

                                  

                                    

                                        type: "person",
                                    

                                  

                                  

                                    

                                        test: function(event) {
                                    

                                  

                                  

                                    

                                          $("#log").append( this.type + " " );
                                    

                                  

                                  

                                    

                                        }
                                    

                                  

                                  

                                    

                                      };
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                      
                                        /* execute you.test() in the context of the `you` object */
                                      
                                    

                                  

                                  

                                    

                                      
                                        /* no matter where it is called */
                                      
                                    

                                  

                                  

                                    

                                      
                                        /* i.e. the `this` keyword will refer to `you` */
                                      
                                    

                                  

                                  

                                    

                                      var youClick = $.proxy( you.test, you );
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                      
                                        /* attach click handlers to #test */
                                      
                                    

                                  

                                  

                                    

                                      $("#test")
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                        /* this === "zombie"; handler unbound after first click */
                                    

                                  

                                  

                                    

                                        .on( "click", $.proxy( me.test, me ) )
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                        /* this === "person" */
                                    

                                  

                                  

                                    

                                        .on( "click", youClick )
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                        /* this === "zombie" */
                                    

                                  

                                  

                                    

                                        .on( "click", $.proxy( you.test, me ) )
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                        /* this === "<button> element" */
                                    

                                  

                                  

                                    

                                        .on( "click", you.test );
                                    

                                  

                                  

                                    

                                      
                                        </script>
                                      
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                      
                                        </body>
                                      
                                    

                                  

                                  

                                    

                                      
                                        </html>

Example: Enforce the context of the function using the "context, function name" signature. Unbind the handler after first click.

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                                        <!DOCTYPE html>
                                      
                                    

                                  

                                  

                                    

                                      
                                        <html>
                                      
                                    

                                  

                                  

                                    

                                      
                                        <head>
                                      
                                    

                                  

                                  

                                    

                                        <script src="http://code.jquery.com/jquery-latest.js"></script>
                                    

                                  

                                  

                                    

                                      
                                        </head>
                                      
                                    

                                  

                                  

                                    

                                      
                                        <body>
                                      
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                        <p><button id="test">Test</button></p>
                                    

                                  

                                  

                                    

                                        <p id="log"></p>
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                      
                                        <script>
                                        
                                      
                                    

                                  

                                  

                                    

                                        var obj = {
                                    

                                  

                                  

                                    

                                          name: "John",
                                    

                                  

                                  

                                    

                                          test: function() {
                                    

                                  

                                  

                                    

                                            $("#log").append( this.name );
                                    

                                  

                                  

                                    

                                            $("#test").off("click", obj.test);
                                    

                                  

                                  

                                    

                                          }
                                    

                                  

                                  

                                    

                                        };
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                        $("#test").on( "click", jQuery.proxy( obj, "test" ) );
                                    

                                  

                                  

                                    

                                      
                                        </script>
                                      
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                      
                                        </body>
                                      
                                    

                                  

                                  

                                    

                                      
                                        </html>

Example: Change the context of a function bound to the click handler,

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                                        <!DOCTYPE html>
                                      
                                    

                                  

                                  

                                    

                                      
                                        <html>
                                      
                                    

                                  

                                  

                                    

                                      
                                        <head>
                                      
                                    

                                  

                                  

                                    

                                        <script src="http://code.jquery.com/jquery-latest.js"></script>
                                    

                                  

                                  

                                    

                                      
                                        </head>
                                      
                                    

                                  

                                  

                                    

                                      
                                        <body>
                                      
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                      <p><button type="button" id="test">Test</button></p>
                                    

                                  

                                  

                                    

                                      
                                        <div id="log">
                                        </div>
                                      
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                      
                                        <script>
                                        
                                      
                                    

                                  

                                  

                                    

                                      var me = {
                                    

                                  

                                  

                                    

                                        /* I'm a dog */
                                    

                                  

                                  

                                    

                                        type: "dog",
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                        /* Note that event comes *after* one and two */
                                    

                                  

                                  

                                    

                                        test: function(one, two, event) {
                                    

                                  

                                  

                                    

                                          $("#log")
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                            /* `one` maps to `you`, the 1st additional */
                                    

                                  

                                  

                                    

                                            /* argument in the $.proxy function call */
                                    

                                  

                                  

                                    

                                            .append( "<h3>Hello " + one.type + ":</h3>" )
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                            /* the `this` keyword refers to `me` */
                                    

                                  

                                  

                                    

                                            /*(the 2nd, context, argument of $.proxy) */
                                    

                                  

                                  

                                    

                                            .append( "I am a " + this.type + ", " )
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                            /* `two` maps to `they`, the 2nd additional */
                                    

                                  

                                  

                                    

                                            /* argument in the $.proxy function call */
                                    

                                  

                                  

                                    

                                            .append( "and they are " + two.type + ".<br>" )
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                            /* the event type is "click" */
                                    

                                  

                                  

                                    

                                            .append( "Thanks for " + event.type + "ing " )
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                            /* the clicked element is `event.target`, */
                                    

                                  

                                  

                                    

                                            /* and its type is "button" */
                                    

                                  

                                  

                                    

                                            .append( "the " + event.target.type + "." );
                                    

                                  

                                  

                                    

                                        }
                                    

                                  

                                  

                                    

                                      };
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                      var you = { type: "cat" };
                                    

                                  

                                  

                                    

                                      var they = { type: "fish" };
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                      
                                        /* Set up handler to execute me.test() in the context */
                                      
                                    

                                  

                                  

                                    

                                      
                                        /* of `me`, with `you` and `they` as additional arguments */
                                      
                                    

                                  

                                  

                                    

                                      var proxy = $.proxy( me.test, me, you, they );
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                      $("#test")
                                    

                                  

                                  

                                    

                                      .on( "click", proxy );
                                    

                                  

                                  

                                    

                                          </script>
                                    

                                  

                                  

                                    

                                       
                                    

                                  

                                  

                                    

                                      
                                        </body>
                                      
                                    

                                  

                                  

                                    

                                      
                                        </html>
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