undefined function when calling javascript prototype method

Question

i have the following javascript object:

var Playlist = function(callback) {
    $.ajax({
        url:'/playlist'
    })
    .done(function(data) {
        this.html = data;
        callback({},this);
    })
    .fail(function(err) {
        callback(err,{});
    });
};

for this object, i declared a prototype method:

Playlist.prototype = {
    render : function() {
        $('#main').html(this.html);
    }
};

now, when i create a new object und try to call the 'render' function like this

function renderPlaylist() {
    var playlist = new Playlist(function(err, obj) {
        obj.render();
    });
}

renderPlaylist();

i get a 'undefined is not a function'. it seems not to know the render function, which i declared in the prototype. what am i missing here? thanks for help.

callback({},this); the this is not what you think. See JavaScript “this” keyword, MDN this documentation and How do JavaScript closures work? — Volune
– Volune, Commented Sep 6, 2014 at 12:30

Community · Accepted Answer · 2017-05-23 12:10:53Z

1

with the help of Volune, i changed my constructor to

var Playlist = function(callback) {
    var playlist = this;
    $.ajax({
        url:'/mpdplaylist'
    })
    .done(function(data) {
        playlist.html = data;
        callback(null,playlist);
    })
    .fail(function(err) {
        callback(err,{});
    });
};

now it works. thank you!!

edit: as Volune pointed out, i replaced the empty object for the error with null in the 'done' callback function

edited May 23, 2017 at 12:10

CommunityBot

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answered Sep 6, 2014 at 12:38

Hinrich

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1 Comment

Volune Over a year ago

If you're using callbacks the same way as NodeJS, you should do callback(null,playlist);. This way the callback can more easily check if there were an error.

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