What does "options = options || {}" mean in Javascript?

javascript syntax notation
ptrn picture ptrn · May 17, 2010 · Viewed 9.7k times · Source

I came over a snippet of code the other day that I got curious about, but I'm not really sure what it actually does;

options = options || {};

My thought so far; sets variable options to value options if exists, if not, set to empty object.

Yes/no?

Answer

Christian C. Salvadó picture Christian C. Salvadó · May 17, 2010

This is useful to setting default values to function arguments, e.g.:

function test (options) {
  options = options || {};
}

If you call test without arguments, options will be initialized with an empty object.

The Logical OR || operator will return its second operand if the first one is falsy.

Falsy values are: 0, null, undefined, the empty string (""), NaN, and of course false.

ES6 UPDATE: Now, we have real default parameter values in the language since ES6.

function test (options = {}) {
  //...
}

If you call the function with no arguments, or if it's called explicitly with the value undefined, the options argument will take the default value. Unlike the || operator example, other falsy values will not cause the use of the default value.

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