babel/doc/playground.md

Playground

Playground is a proving ground for possible ES7 proposals.

NOTE: These features are in no way endorsed by Ecma International and are not a part of ES6. They might become a part of ECMAScript in the future.

Usage

$ 6to5 --playground

to5.transform("code", { playground: true });

NOTE: Enabling playground also enables experimental support.

Features

• Memoization operator
• Method binding

Memoization assignment operator

var obj = {};
obj.x ?= 2;
obj.x; // 2

obj = { x: 1 };
obj.x ?= 2;
obj.x; // 1

obj = { x: undefined }
obj.x ?= 2;
obj.x; // undefined

var obj = {};
obj.x ?= 2;

equivalent to:

var obj = {};
if (Object.prototype.hasOwnProperty.call(obj, "x")) obj.x = 2;

Method binding expression

var fn = obj:method;
var fn = obj:method("foob");

equivalent to:

var fn = obj.method.bind(obj);
var fn = obj.method.bind(obj, "foob");

NOTE: Method binding can only be used as an expression and not as statement.