javascript calling the function from prototype

Question

I am learning javascript. When I call pictureArrayAdd method I receive error Picture.pictureArrayAdd is not a function. Why?

window.onload = init;
//window.picture = new Array();

function init() {
    var button = document.getElementById("addButton");
    button.onclick = addPicture;
}

function Picture() {};

Picture.prototype = {
    pictureArray: [],
    pictureArrayAdd: function(newImage) {
        this.pictureArray.push(newImage);
        return this

    }
}


var addPicture = function() {
    var textInput = document.getElementById ("pictureName");
    var newPicture = textInput.value;
    Picture.pictureArrayAdd(newPicture);

}

You'll want to create an instance: var picture = new Picture(); picture.pictureArrayAdd(...). Otherwise, you don't need a constructor if you just want a singleton: var Picture = {...}; — Jonathan Lonowski
– Jonathan Lonowski, Commented Jan 27, 2014 at 17:23
Try new Picture.pictureArrayAdd(newPicture) Protoype stuff are accesible from function instances using 'new' — blessanm86
– blessanm86, Commented Jan 27, 2014 at 17:24

DontVoteMeDown · Accepted Answer · 2014-01-27 17:31:31Z

3

You have to initialize an instace of your object:

var addPicture = function() {
    var textInput = document.getElementById ("pictureName");
    var newPicture = textInput.value;
    var pic = new Picture();
    pic.pictureArrayAdd(newPicture);
}

Besides - just a tip -, you can use a optional parameter on your constructor, like this:

function Picture(newImage) {
    if (newImage != undefined) {
        this.pictureArrayAdd(newImage);
    }
};

So you have a shortcut to your pictureArrayAdd function:

var pic = new Picture("picture1.png");

See it working here.

edited Jan 27, 2014 at 17:31

answered Jan 27, 2014 at 17:23

DontVoteMeDown

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