ecmascript 6 - Javascript object literal: what exactly is {a, b, c}?

Question

The question I have is best given by way of this jsfiddle, the code for which is below:

var a = 1, b = 'x', c = true;

var d = {a: a, b: b, c: c}; // <--- object literal
var e = [a, b, c];          // <--- array
var f = {a, b, c};          // <--- what exactly is this??

// these all give the same output:
alert(d.a  + ', ' + d.b +  ', ' + d.c );
alert(e[0] + ', ' + e[1] + ', ' + e[2]);
alert(f.a  + ', ' + f.b +  ', ' + f.c );

What sort of a data structure is f? Is it just a shorthand for d?

Answer 1

var f = {a, b, c};

It came with ES6 (ECMAScript 2015) and means exactly the same as:

var f = {a: a, b: b, c: c};

It is called Object Literal Property Value Shorthands (or simply property value shorthand, shorthand properties).

You can also combine shorthands with classical initialization:

var f = {a: 1, b, c};

For more information see Object initializer.