Question

When using object constructors, properties can be directly assigned to the value of previously defined properties:

var foo = new (function() {
   this.bar = 5;
   this.baz = this.bar;
})();
alert(foo.baz) // 5

I would like to refer to a previously defined property within an OBJECT LITERAL:

var foo = {
   bar : 5,
   baz : bar
}
alert (foo.baz) // I want 5, but evaluates to undefined

I know that I could do this:

var foo = {
   bar : 5,
   baz : function() {
      alert(this.bar); // 5
   }

But I want to assign baz directly to a value rather than a function. Any ideas?

Answer 1

You can also just build a literal by parts:

var foo = {bar:5};
foo.baz = foo.bar;

If you need to fit this inside an expression (instead of through multiple statements) you can try abusing the comma operator or you can make a helper function:

(Warning: untested code)

function make_fancy_object(base_object, copies_to_make){
     var i, copy_from, copy_to_list;
     for(copy_from in copies_to_make){
         if(copies_to_make.hasOwnProperty(copy_from)){
             copy_to_list = copies_to_make[copy_from];
             for(var i=0; i<copy_to_list.length; i++){
                 base_object[copy_to_list[i]] = base_object[copy_from];
             }
          }
      }
}

var foo = make_fancy_object(
    {bar: 5},
    {bar: ["baz", "biv"]}
);

//foo.baz and foo.biv should be 5 now as well.