#esnext

Getting object property paths can be tricky on complex objects, because just one property being empty will trigger an error. For example, when getting page menu data from an API:

function getPageMenu() { return [ { title: 'Dashboard', location: { fullUrl: 'https://my-website.com/dashboard/user1', shortUrl: 'https://goo.gl/929okH' } }, { title: 'Logout', // No location since it redirects to a login page } ] } function printAllPageLinks() { const pageMenuData = getPageMenu(); for (let page of pageMenuData) { // Error here console.log(page.location.fullUrl); } } printAllPageLinks();

There will be an error with the console.log above. Normally, these links would be used in a UI, but this is just for example purposes. To avoid this, the && syntax can be used:

function printAllPageLinks() { const pageMenuData = getPageMenu(); for (let page of pageMenuData) { console.log(page.title, page.location && page.location.fullUrl); } }

This is ok, but it is verbose and will look confusing to anyone not very familiar with Javascript as this syntax does not appear in any other very popular languages (that I am aware of). Instead, a get function can be used from Lodash (there are similar alternatives in many other utility libraries):

function printAllPageLinks() { const pageMenuData = getPageMenu(); for (let page of pageMenuData) { console.log(page.title, _.get(page, 'location.fullUrl')); } }

The processing will be slower due to the interpretation of the string properties, but that is the only drawback. For the most part this level of efficiency will not matter. Since the implentation for the above is complex (e.g. it should support arrays too), I will not be showing a simple example like usual.

Finally, there is a JavaScript feature proposal called Optional Chaining in the works for language syntax support. Just keep in mind it is early in the process being stage 1 and may never actually make it into the language:

function printAllPageLinks() { const pageMenuData = getPageMenu(); for (let page of pageMenuData) { console.log(page.title, page.?location.?fullUrl); } }

Somewhat recently, I was looking through some example code (JavaScript) for a project and I came across the following syntax: function someFunction() { return { dog: "woof", cat: "meow", bird: "chirp", }[bird]; } I hadn’t seen this format before so it took me a second to parse through what it was doing. Essentially, this is just a fancy way of returning a single value from within an unnamed…

ECMAScript6에서 필요한 파라미터 처리

ECMA5에서, 당신은 필요한 파라미터의가 제공되어지는 보증을 위해 몇가지 옵션을 했고, 불안정하고 우아하지 못한 모든것을

불안정하고 우아하지 못한 모든 것에 대해 필요한 매개변수를 제공되어졌고, 보증을 위해 몇가지 옵션을 가진다.

function foo(mustBeProvided) { if (arguments.length < 1) throw new Error(...) if (! (0 in arguments)) ... if (mustBeProvided === undefined) ... }

ECMAScript6에서는 더 간결한 코드 달성 가능한 기본 파라미터를 사용할 수 있다.

UPDATE! 3rdEden has pointed out that it's possible to get harmony in node 0.6

You can get it by using a flag when invoking node through the command line

node --harmony_typeof --harmony_block_scoping --harmony_proxies --harmony_weakmaps file.js

Or if you're using node 0.7.x

node --harmony file.js

Harmony!!!!1

Enable ECMAScript’s new features and syntax in node point javascript.

Node unstable has just been released and with that V8 has been upgraded to 3.8.6 which contains flags for experimental language features.

By default those flags are turned off, but you can always turn them on. Here’s how:

Download node 0.7.0.

If you’ve got it cloned on git run a git fetch and then git checkout v0.7.0 otherwise read the release notes for instructions on where to download.

Set harmony flag to true in V8

Once you’ve got the source code, open up deps/v8/src/flag-definitions.h and look for Line 115

Change the flag from false to true.

DEFINE_bool(harmony, true, "enable all harmony features")

Compile Node

./configure && make && make install

Have fun!

function foo() { "use strict"; let i = -1; for (let i = 0; i < 10; i += 1) { console.log(i); // 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 } console.log(i); // -1 } foo();

NOTE: you’ll need to use "use strict"; otherwise the code above will not run.

By doing this you’ll get:

Sets, Maps, and Weak Maps

Block scoping

Proxies

New typeof semantics