- Let as block-scoped var, const for constant variable declarations
- Compact function syntax: function(x) { return x * x } becomes #(x) { x * x } (including an implicit return)
- arguments is replaced by rest parameters and default arguments (see below).
- Records: read-only objects (no Object.freeze()). #{x: 10, y: 20}
- Tuples: read-only arrays with slicing and negative indices that access elements at the end. #[1, 2, 3][-1] → 3
- Paren-free syntax for if.
- Modules: The simple modules proposal will probably make it into Harmony.
- Iteration: Lots of cool stuff, inspired by Python.
for k in keys(o) { append(o[k]) } for v in values(o) { append(v) } for [k,v] in items(o) { append(k, v) } for x in o { append(x) } #sqgen(n) { for i in range(n) yield i*i } // a function return [i * i for i in range(n)] return (i * i for i in range(n)) - Rest parameters: function printf(format, ...args) { ... }
- Default parameter values: function add(left, right=1) {...}
- Spread: the analog to rest parameters. f(...myArray)
- Destructuring assignments for arrays and objects. The latter takes some getting used to.
let [first, second] = sequence const {name, address, ...misc} = person
My own wishes:
- Self-style full prototypal inheritance (not much different from how JS is now).
- Handle this like Lua: obj.method(a,b) should be syntactic sugar for m(obj, a, b) (where m is the function stored in obj.method).
- Python-style keyword arguments (but I do agree with a comment made by Eich that destructuring makes them less urgent).
- Turn "class methods” such as Object.keys() into instance methods: Instead of Object.keys(foo), I’d like to use foo.keys().
- if statement: I would make braces mandatory and introduce an elsif keyword (could also be named else if)
- Implicit returns: It would be nice if the same could be done for if-then-else (i.e., it becomes an expression). No more ternary if operator!
- I’ve critiqued CoffeeScript’s syntax and compared it to JS without parens.
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