Top Posts Tagged with #ecma6

Angular 2 그리고 웹 프론트엔드 (1/2)

한동안 마무리 지어야 하는 일때문에 정신이 없다가 이제서야 정리를 할 시간이 오게 되었다..

이 포스트에서는 Angular가 무엇인지 모르는 분들을 위해 Angular를 설명하는 내용을 채울까 한다.

Angular 2 그리고 웹 프론트엔드 (1/2) - 현재 글

Angular 2 그리고 웹 프론트엔드 (2/2)

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At the end of July 2014, TC39 [1] had another meeting, during which the last details of the ECMAScript 6 (ES6) module syntax were finalized. Some examples from the full post are included below.

Named Exports:

//------ lib.js ------ export const sqrt = Math.sqrt; export function square(x) { return x * x; } export function diag(x, y) { return sqrt(square(x) + square(y)); } //------ main.js ------ import { square, diag } from 'lib'; console.log(square(11)); // 121 console.log(diag(4, 3)); // 5

Default Exports

//------ myFunc.js ------ export default function () { ... }; //------ main1.js ------ import myFunc from 'myFunc'; myFunc();

#programming #javascript #ecma6 #modules #commonjs

Let and Const: ES6 scope now.

One of the features I'm most excited about for ES6 (besides arrow funcs, can't fucking wait for those) are the introduction of let and const as alternatives to var.

In case you don't program in JavaScript (because if you do you should know this), JavaScript variables are functionally scoped not block scoped like most other languages. This can trip up even experienced programmers from time to time especially when combined with hoisting.

https://gist.github.com/calvinmetcalf/6275306

This is fixed in ES6 with let, which acts just like var except it's block scoped

https://gist.github.com/calvinmetcalf/6275358

Now let isn't what I'm exited about really, I'm excited for let's cousin, const, const is like let except you can't change it latter. Before you dismiss the idea of variables that aren't variable. Look at your code, with the exception of loops most of my variables don't change much at all. My more functional libraries that use map and forEach a lot almost never modify variables, they wouldn't use let at all. Some languages like Erlang only have variables in the const style, as Erlang was the first language I learned this does bias me a bit.

At the you have a few choices for using these in your code, in node you can use the '--harmony' flag and use this in all your node code (you need to be in strict mode), this is what I did for a tile server I wrote recently, this one actually runs on the command line as well, which required a bit of a hack.

For browsers I recently converted catiline.js to use these, thanks to a nice library called defs which uses esprima to parse and rewrite your code. Which nicely throws an error if you try to redefine a const.

While I have nothing to base what I'm about to say on, I'd predict that once browsers start implementing let and const. Using const will speed up your code as browsers will be able to optimize those values in memory, unless having to check that those values don't change ends up slowing them down, it could go either way.

#js #javascript #ecma6 #es6 #let #const