ECMAScript的新特性

ECMAScript 5相对于ECMAScript 3的新特性：

• Getter/setters
• Trailing commas in array and object literals
• Reserved words as property names
• New Object methods (create, defineProperty, keys, seal, freeze, getOwnPropertyNames, etc.)
• New Array methods (isArray, indexOf, every, some, map, filter, reduce, etc.)
• String.prototype.trim and property access
• New Date methods (toISOString, now, toJSON)
• Function bind
• JSON
• Immutable global objects (undefined, NaN, Infinity)
• Strict mode
• Other minor changes (parseInt ignores leading zeroes, thown functions have proper this values, etc.)

ECMAScript 6相对于ECMAScript 5的新特性：

• Let (lexical) and const (unrebindable) bindings
• Arrow functions (shorter anonymous functions) and lexical this (enclosing scope this)
• Classes (syntactic suger on top of prototypes)
• Object literal improvements (computed keys, shorter method definitions, etc.)
• Template strings
• Promises
• Generators, iterables, iterators and for..of
• Default arguments for functions and the rest operator
• Spread syntax
• Destructuring
• Module syntax
• New collections (Set, Map, WeakSet, WeakMap)
• Proxies and Reflection
• Symbols
• Typed arrays
• Support for subclassing built-ins
• Guaranteed tail-call optimization
• Simpler Unicode support
• Binary and octal literals