Question

I want to create an object with a non-enumerable property(a property that does not show up in a for (var x in obj loop). Is it possible to do this?

Answer 1

It isn’t possible in ECMAScript 3 (which was what the major browsers implemented at the time this question was asked in 2010). However, in ECMAScript 5, which current versions of all major browsers implement, it is possible to set a property as non-enumerable:

var obj = {
   name: "Fred"
};

Object.defineProperty(obj, "age", {
    enumerable: false,
    writable: true
});

obj.age = 75;

/* The following will only log "name=>Fred" */
for (var i in obj) {
   console.log(i + "=>" + obj[i]);
}

This works in current browsers: see http://kangax.github.com/es5-compat-table/ for details of compatibility in older browsers.

Note that the property must also be set writable in the call to Object.defineProperty to allow normal assignments (it’s false by default).