Dynamically create Instance fields for a JavaScript Object

Question

I have a dynamically-created list of strings called 'variables'. I need to use these strings as the instance variables for an array of JavaScript objects.

var objectsArr  = [];
function obj(){};

for (var i=0; i<someNumberOfObjects; i++ ) {
    ...
    objectsArr[i] = new Object();           


    for (var j=0; j<variables.length; j++) {
        objectArr[i].b = 'something';  //<--this works, but...
        //objectArr[i].variables[j] = 'something';  //<---this is what I want to do.
    }       
}

The commented-out line shows what I am trying to do.

Kirk Woll · Accepted Answer · 2011-09-06 03:28:31Z

9

You can use the bracket syntax to manipulate the property by name:

objectArr[i][variables[j]] = 'something';

In other words, get the object from objectArr at index i then find the field with name variables[j] and set the value of that field to 'something'.

In general terms, given object o:

var o = {};

You can set the property by name:

o['propertyName'] = 'value';

And access it in the usual way:

alert(o.propertyName);

edited Sep 6, 2011 at 3:28

answered Sep 6, 2011 at 3:17

Kirk Woll

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1 Comment

John R Over a year ago

That did it. Thanks you for the fast reply.

FishBasketGordo · Accepted Answer · 2011-09-06 03:24:03Z

0

Use the bracket notation. This will get it done:

var objectsArr = [], ii, jj;

function Obj() {}

for(ii = 0; ii < someNumberOfObjects; ii += 1) {
    objectsArr[ii] = new Obj();            

    for (jj = 0; jj < variables.length; jj += 1) {
        objectArr[ii][variables[jj]] = 'something';
    }       
}

A couple of additional notes:

Javascript doesn't have block scope, so you must have two separate loop variables.
By convention, constructor functions like Obj should begin with a capital letter to signify that they ought to be used with the new keyword. In this case though, unless you need the objects to have a non-Object prototype, you could just use a plain object literal (objectsArr[ii] = {};).

answered Sep 6, 2011 at 3:24

FishBasketGordo

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