Is there a built in method to merge the properties of two objects into a single object?

Question

I'm looking for a built-in method that combines two associative arrays or objects into one. Using webkit in Adobe Air if that makes a difference. But basically I have two objects or associative arrays if you will:

var obj1 = { prop1: "something", prop2 "anotherthing" };
var obj2 = { prop3: "somethingelse" };

and I want to do merge them and create an object that has all the combined keys and values of the above two objects:

var obj3 = obj1.merge( obj2 ); //something similar to array's concat maybe?

alert(obj3.prop1); //alerts "something"
alert(obj3.prop2); //allerts "anotherthing"
alert(obj3.prop3); //alerts "somethingelse"

Any built in function that does this or do I have to manually do it?

Answer 1

There is no built-in method. Several libraries provide a method to do what you describe.

Writing one yourself is straightforward:

var merge = function(dest, source){
    // This will resolve conflicts by using the source object's properties
    for (prop in source){
        dest[prop] = source[prop];
    }
}

// Use like so
merge(obj1, obj2);

edit: no longer modifying Object.prototype, which is dangerous and generally frowned upon.

Answer 2

An alternative implementation to Triptych's (which is essentially the same as Prototype's extend method) is:

/** returns object with properties of both object1 and object2. 
  *  if a collision occurs, properties of object1 take priority
  */
function merge(object1,object2) {
    var retObj = {};
    for (prop in object2){
        retObj[prop] = object2[prop];
    }
    for (prop in object1){
        retObj[prop] = object1[prop];
    }
    return retObj;
}

This doesn't modify the prototype of Object and thus doesn't have it's not insignificant drawbacks.

Answer 3

Like tryptych said, except that his example code (was dangerous and wrong, until he edited it). something a little more like the following would be better.

mylib = mylib || {};
//take objects a and b, and return a new merged object o;
mylib.merge = function(a, b) {

  var i, o = {};
  for(i in a) {
      if(a.hasOwnProperty(i)){
          o[i]=a[i];
      }
  }
  for(i in b) {
      if(b.hasOwnProperty(i)){
          o[i]=b[i];
      }
  }

  return o;

}
//take objects a and b, and modify object a to have b's properties
mylib.augment = function(a, b) {
  var i;
  for(i in b) {
      if(b.hasOwnProperty(i)){
          a[i]=b[i];
      }
  }
  return a;
}

edit re: ferocious. Deep copy is a different, and orthogonal function to this, but just for you, here's my personal deep copy function

   function clone(o) {
    var t,i;
    if (o === undefined) {
        return undefined;
    }
    if (o === null) {
        return null;
    }
    if (o instanceof Function) {
        return o;
    }
    if (! (o instanceof Object)) {
        return o;
    } else {
        t = {};
        for (i in o) {
            /* jslint complains about this, it's correct in this case. I think. */
            t[i] = clone(o[i]);
        }
        return t;
    }
   }