Friday, February 17, 2012

JS Object, how to access objects from within myself


So, i see no reason why this isn't working but i am at a wall and frustrated. Why can't i call this.myself from within the wyr.message.close function? Maybe my understanding of this is scewed but i was sure this is referring to the object itself, not the function.




this.myself is undefined



Code:




wyr.message = {
myself: $('.message'),
init: function() {
if(this.myself.is(':visible')){
setTimeout(this.close, 5000);
}
},
close: function(){
this.myself.fadeOut(1200,function(){
this.myself.remove();
});
}
}

2 comments:

  1. wyr.message = {
    myself: $('.message'),
    init: function() {
    var self = this;
    if(this.myself.is(':visible')){
    setTimeout(function(){
    self.close();
    }, 5000);
    }
    },
    close: function(){
    this.myself.fadeOut(1200,function(){
    $(this).remove();
    });
    }
    }


    The issue is context. Within the callback function passed to fadeOut, this is bound to the element being worked on by jQuery, not to the wyr.message object.

    EDIT:

    There's also an issue with the init method. SetTimeout will bind the value of this to the global (window) object - so we save a reference to the this we want and use that to invoke the close method.

    You could also look into Function.prototype.bind, but it's not supported in older browsers.

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  2. First, javascript object literal property expressions are evaluated at the time you create the object instance. myself will be whatever that selector grabs at that time, which is probably nothing. The myself property needs to be a function if you want it to return the value of $('.message') at the time of invocation. As a consequence you'll need to change all uses to function calls as well.

    Second, during the execution of the setTimeout callback, this is bound to the window object, so you need to qualify it appropriately:

    wyr.message = {
    myself: function() { return $('.message'); },
    init: function() {
    if(this.myself().is(':visible')){
    setTimeout(this.close, 5000);
    }
    },
    close: function(){
    message.myself().fadeOut(1200,function(){
    $(this).remove();
    });
    }
    };


    (Note, this will fade out and remove everything matching the selector when the timeout fires.)

    ReplyDelete