ES6: Features By Testing

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kyle simpson http://getify.me @getify ES6: features by testing

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ES6/2015

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Block-Scoped Declarations Spread / Rest Default Parameter Values Destructuring Object Literal Extensions Template Literals Arrow Functions `for..of` Loops Regular Expression Extensions Number Literal Extensions Unicode Symbols Iterators Generators Modules Classes

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Promises Generators + Promises Typed Arrays Maps WeakMaps Sets WeakSets `Array` `Object` `Math` `Number` `String` Function Names Meta Properties Well Known Symbols Proxies `Reflect` API Tail Call Optimization (TCO)

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the hype

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arrow functions

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arrow functions

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arrow functions • will it ever need this/super? • will it ever need a lexical name? • will it ever need more than one statement? • will its return have side effects? • are all the syntax variances really readable/obvious? caveats

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arrow functions

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the substance

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array spread :(

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array spread \o/

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array spread :(

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array spread \o/

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array gather (aka "rest") :(

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array gather (aka "rest") \o/

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parameter defaults :(

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parameter defaults \o/

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destructuring :(

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destructuring & concise properties :/

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destructuring & concise properties whitespace / indentation ftw \o/

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destructuring (renaming/defaults) :(

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destructuring (renaming/defaults) \o/

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destructuring & restructuring

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destructuring & restructuring :(

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\o/ destructuring & restructuring

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async: promises & generators :(

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async: promises & generators :/

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async: promises & generators github.com/getify/asynquence \o/

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\o/ async: promises & generators

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\o/ async: promises & generators

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\o/ async: promises & generators

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async: promises & generators async functions (es7'ish) \o/

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:/ async: promises & generators

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\o/ async: promises & generators

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iterators :(

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iterators \o/

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iterators :/

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\o/ iterators

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excited yet!?

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ES6 browsers are ubiquitous, right? not exactly. :(

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transpiling ftw \o/

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polyfills ftw \o/

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github.com/paulmillr/es6-shim

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what features do you need?

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96% of all JS programs need less than 37% of ES6 *totally made up * *

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Microsoft Edge 0.11.10074.0 Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/39.0.2171.71 Safari/537.36 Edge/12.0

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transpiling & polyfilling: can't • several well-known symbols • subclassing natives • __proto__ • tail call optimization (rewriting to tail calls can) https://wpdev.uservoice.com/forums/257854-microsoft-edge-developer/ suggestions/6850816-es6-tail-call-optimization • others... caveats

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transpiling ftl polyfills ftl :(

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feature testing ftw \o/

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feature testing: APIs

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feature testing: syntax

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feature testing: syntax

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https://FeatureTests.io

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https://FeatureTests.io

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demo

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don't shy away from ES6+, start using these features now

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ongoing gap

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don't serve code on the trailing edge of that gap

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transpiling & polyfilling => developing for the current & future

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serve the right code for the right browser

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blog.getify.com/smarter-transpilation-strategy

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kyle simpson http://getify.me @getify thanks! https://github.com/getify/You-Dont-Know-JS/blob/master/es6%20& %20beyond/README.md#you-dont-know-js-es6--beyond