Question

I have object literal what I consider as base object:

var obj = {
   key1   : 'value1',
   key2   : 'value2'
}

and would like to use this object and pass it to function with extention like

myFunction( obj + { key3 : 'value3' } );

// param became:
{
   key1   : 'value1',
   key2   : 'value2',
   key3   : 'value3'
}

or

myFunction( obj + { key2 : 'new value2' } );

// param became:
{
   key1   : 'value1',
   key2   : 'new value2'
}

+ operator is not correct for it. How I can do it? Is it a way ?

EDIT: Do you want to permanently alter obj? – No, I would like to able to reuse it for next call as base.

Answer 1

If you’re okay with altering obj, just change it before you pass it:

var obj = { /* stuff */ };

obj.key3 = 'value3';
myFunction(obj);

---

Do you want to permanently alter obj? – No, I would like to able to reuse it for next call as base.

Okay, so you need to make a copy of obj, and alter the copy — either before you call myFunction:

var obj = { /* stuff */ };
var extension = {key3: 'value3'};

myFunction($.extend({}, obj, extension));

or pass obj and the “extension” to myFunction:

var obj = { /* stuff */ };
var extension = {key3: 'value3'};

myFunction(obj, extension);

and have myFunction do the work:

function myFunction(base, ext)
{
    if (typeof base === 'object' && typeof ext === 'object')
    {
        base = $.extend({}, base, ext);
    }

    // rest of the function logic here
}

If you’re already (or don’t mind) using jQuery, $.extend() will be your best friend for the task.