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How can I merge 2 javascript objects, populating the properties in one if they don't exist in the other?

rated 0 times [ 14] [ 3] / answers: 1 / hits: 18668 / 15 Years ago, fri, may 22, 2009, 12:00:00

If I have a javascript object/assoc. array defined like this:

function somefunction(options) {



    var defaults = {

        prop1: 'foo',

        prop2: 'bar'

    };



    //Do stuff here



}

and I want to use this as the default values for the function. So when the function gets called I want to populate the options variable with the values in defaults, but only if they don't exist in options.

So lets say that this was called

somefunction({ prop1: 'fish' });

How can I make it so that options gets merged with defaults such that I get this

{

    prop1: 'fish',

    prop2: 'bar'

}

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answered 15 Years ago mckinleyi · Accepted Answer

You could look at either jQuery's or Prototypes extend functionality.

It looks like this: (taken directly from jQuery)

jQuery.extend = jQuery.fn.extend = function() {

    // copy reference to target object

    var target = arguments[0] || {}, i = 1, length = arguments.length, deep = false, options;



    // Handle a deep copy situation

    if ( typeof target === boolean ) {

        deep = target;

        target = arguments[1] || {};

        // skip the boolean and the target

        i = 2;

    }



    // Handle case when target is a string or something (possible in deep copy)

    if ( typeof target !== object && !jQuery.isFunction(target) )

        target = {};



    // extend jQuery itself if only one argument is passed

    if ( length == i ) {

        target = this;

        --i;

    }



    for ( ; i < length; i++ )

        // Only deal with non-null/undefined values

        if ( (options = arguments[ i ]) != null )

            // Extend the base object

            for ( var name in options ) {

                var src = target[ name ], copy = options[ name ];



                // Prevent never-ending loop

                if ( target === copy )

                    continue;



                // Recurse if we're merging object values

                if ( deep && copy && typeof copy === object && !copy.nodeType )

                    target[ name ] = jQuery.extend( deep, 

                        // Never move original objects, clone them

                        src || ( copy.length != null ? [ ] : { } )

                    , copy );



                // Don't bring in undefined values

                else if ( copy !== undefined )

                    target[ name ] = copy;



            }



    // Return the modified object

    return target;

};