Javascript: Accessing array inside an object

Question

I have an array cornerId inside an object elementMatrix. Thereafter I want to create elemArray which is an array of the object elementMatrix. However I am not able to access the value of cornerId.

function elementMatrix() {
    var cornerId=new Array();
}

var elemArray=new Array();
elemArray[0]=new elementMatrix();
elemArray[0].cornerId[0]="z"; //if I put elemArray[0].cornerId="z"; then it works for the first element - but then how do I put second element???
elemArray[0].cornerId[1]="a";
alert(elemArray[0].cornerId[0]); // shows undefined
alert(elemArray[0].cornerId[1]); //again undefined
....
Add other elemArray values
....

I want to assign values and access values for the nth position of the array cornerId, which is a part of elemArray which is an array of object elementMatrix. Can anyone show me the right way to access cornerId values???

EDIT:

To clarify I want the liberty to add cornerId at the nth position (overwrite existing value) and not push it. Also I had not asked this originally but if there is a method to remove an nth position from cornerId then that will be great.

silly · Accepted Answer · 2012-12-19 07:42:05Z

define your corner with this, push on arrays.... like this

function elementMatrix() {
    this.cornerId = [];
};
var elemArray = [];
var newMatrix =new elementMatrix();
newMatrix.cornerId.push('z');
newMatrix.cornerId.push('a');
elemArray.push(newMatrix);

alert(elemArray[0].cornerId[0]);
alert(elemArray[0].cornerId[1]);

or you can make your cornerid private and return public method like this (add is fluent)

function elementMatrix() {
    var cornerId = [];

    return {
        addCornerId: function(id) {
            cornerId.push(id);
            return this;
        },

        getCornerId: function(pos) {
            if(cornerId.length >= pos) {
                return cornerId[pos];
            }

            return null;
        }
    };
};
var elemArray = [];
var newMatrix =new elementMatrix();
newMatrix
    .addCornerId('z')
    .addCornerId('a');
elemArray.push(newMatrix);

alert(elemArray[0].getCornerId(0));
alert(elemArray[0].getCornerId(1));

edit, if you want a key value pair use a object instead a array like this

function elementMatrix() {
    var cornerId = {};
    var nextKey = 0;

    return {
        addCornerId: function(id, key) {
            if(!key && key !== 0) {
                key = nextKey;
            }
            cornerId[key] = id;
            nextKey++;
            return this;
        },

        removeCornerId: function(key) {
            if(cornerId[key]) {
                  delete cornerId[key]
            }

            return this;
        },
        getCornerId: function(key) {
            if(cornerId[key]) {
                return cornerId[key];
            }

            return null;
        }
    };
};
var elemArray = [];
var newMatrix =new elementMatrix();
newMatrix
    .addCornerId('z')
    .addCornerId('a')
    .addCornerId('XXX', 0)
    .addCornerId('YYYY', 'abc');
elemArray.push(newMatrix);

alert(elemArray[0].getCornerId(0));
alert(elemArray[0].getCornerId('abc'));

Umur Kontacı · Accepted Answer · 2012-12-19 07:08:53Z

2

First, don't use array initializer with new Array() use []; see Douglas Crockford's justification for that.

function elementMatrix() {
    var cornerId=[];
    return {
        cornerId: cornerId
    };
}
var elemArray=[];
elemArray.push(elementMatrix());
elemArray[0].cornerId.push("z");
elemArray[0].cornerId.push("a");
alert(elemArray[0].cornerId[0]);
alert(elemArray[0].cornerId[1]);

answered Dec 19, 2012 at 7:08

Umur Kontacı

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3 Comments

user1517108 Over a year ago

Thats a very quick and a good answer. Just one clarity is there a way to add the element in the nth position rather than push it at the end. Can i push the value at nth cornerId position of elemArray[0] (basically an overwrite). I have edited my question to be more clear.

Umur Kontacı Over a year ago

Of course you can, but since you are changing a value in a specific position, it is not called pushing. myArray[index] = newvalue would do. take a look at w3schools.com

user1517108 Over a year ago

Oh it's embarrasing how simple it was. I was under the impression that I had tried this method and it didnt work. tx a ton

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