Question

Possible Duplicate:
What does “options = options || {}” mean in Javascript?

I stumbled upon this line, and can’t seem to figure out what it means

var G = G || {};

Any ideas?

Answer 1

If G is currently any “falsey” value, then the object literal will be assigned to G.

The “falsey” values are…

• undefined
• null
• ''
• NaN
• false
• 0

The operator being used is the logical OR operator.

The way it works is that it evaluates its left operand first. If that operand has a “truthy” value (any non-falsey value), it returns it, and doesn’t evaluate (short-circuits) the second operand.

If the left operand was “falsey”, then it returns its right operand, irrespective of its value.

---

Example where G is falsey…

//      v--- Evaluate G. The value of G is the "falsey" value undefined...
var G = G || {};
//            ^--- ...so evaluate and return the right hand operand.

Example where G is truthy…

G = 123;

//      v--- Evaluate G. The value of G is a "truthy" value 123...
var G = G || {};
//      ^--- ...so return 123, and do not evaluate the right hand operand.