JavaScript Environment - Amazon Vega Docs

JavaScript runtime

When using React Native for Vega, you will always use Hermes, an open-source JavaScript engine optimized for React Native. On Vega, we don’t support using JavaScriptCore or Chrome (including V8) itself for tasks such as debugging. Hermes is mainly used in the context of React Native and its roadmap follows the versions of React Native. Your Hermes version depends on the React Native version you are using, for example, 0.72.

JavaScript syntax transformers

Syntax transformers make writing code more enjoyable by allowing you to use new JavaScript syntax without having to wait for support on all interpreters. React Native ships with the Babel JavaScript compiler. Check Babel documentation on its supported transformations for more details. A full list of React Native’s enabled transformations can be found in @react-native/babel-preset.

Transformation	Code
ECMAScript 5
Reserved Words	`promise.catch(function() {...});`
ECMAScript 2015 (ES6)
Arrow functions	`<C onPress={() => this.setState({pressed: true})} />`
Block scoping	`let greeting = 'hi';`
Call spread	`Math.max(...array);`
Classes	`class C extends React.Component {render() { return <View />; }}`
Computed Properties	`const key = 'abc'; const obj = {[key]: 10};`
Constants	`const answer = 42;`
Destructuring	`const {isActive, style} = this.props;`
for…of	`for (var num of [1, 2, 3]) {...};`
Function Name	`let number = x => x;`
Literals	`const b = 0b11; const o = 0o7; const u = 'Hello\\u{000A}\\u{0009}!';`
Modules	`import React, {Component} from 'react';`
Object Concise Method	`const obj = {method() { return 10; }};`
Object Short Notation	`const name = 'vjeux'; const obj = {name};`
Parameters	`function test(x = 'hello', {a, b}, ...args) {}`
Rest Params	`function(type, ...args) {};`
Shorthand Properties	`const o = {a, b, c};`
Sticky Regex	`const a = /o+/y;`
Template Literals	`const who = 'world'; const str =` Hello $`;`
Unicode Regex	`const string = 'foo💩bar'; const match = string.match(/foo(.)bar/u);`
ECMAScript 2016 (ES7)
Exponentiation Operator	`let x = 10 ** 2;`
ECMAScript 2017 (ES8)
Async Functions	`async function doStuffAsync() {const foo = await doOtherStuffAsync();};`
Function Trailing Comma	`function f(a, b, c,) {};`
ECMAScript 2018 (ES9)
Object Spread	`const extended = {...obj, a: 10};`
ECMAScript 2019 (ES10)
Optional Catch Binding	`try {throw 0; } catch { doSomethingWhichDoesNotCareAboutTheValueThrown();}`
ECMAScript 2020 (ES11)
Dynamic Imports	`const package = await import('package'); package.function()`
Nullish Coalescing Operator	`const foo = object.foo ?? 'default';`
Optional Chaining	`const name = obj.user?.name;`
ECMAScript 2022 (ES13)
Class Fields	`class Bork {static a = 'foo'; static b; x = 'bar'; y;}`
Stage 1 Proposal
Export Default From	`export v from 'mod';`
Miscellaneous
Babel Template	`template(`const %%importName%% = require(%%source%%);`);`
Flow	`function foo(x: ?number): string {};`
ESM to CJS	`export default 42;`
JSX	`<view style="color: 'red'"></view>`
Object Assign	`Object.assign(a, b);`
React Display Name	`const bar = createReactClass({});`
TypeScript	`function foo(x: {hello: true, target: 'react native!'}): string {};`

Polyfills

Many standard functions are also available on all the supported JavaScript runtimes.

Browser

CommonJS require
[console.{log, warn, error, info, trace, table, group, groupEnd}](https://developer.chrome.com/devtools/docs/console-api)
XMLHttpRequest, fetch
{set, clear}{Timeout, Interval, Immediate}, {request, cancel}AnimationFrame

ECMAScript 2015 (ES6)

Array.from
Array.prototype.{[find](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/find), [findIndex](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/findIndex)}
Object.assign
String.prototype.{[startsWith](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/startsWith), [endsWith](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/endsWith), [repeat](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/repeat), [includes](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/includes)}

ECMAScript 2016 (ES7)

Array.prototype.[includes](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/includes)

ECMAScript 2017 (ES8)

Object.{[entries](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/entries), [values](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/values)}

Specific

__DEV__

​JavaScript runtime

​JavaScript syntax transformers

​Polyfills

​Browser

​ECMAScript 2015 (ES6)

​ECMAScript 2016 (ES7)

​ECMAScript 2017 (ES8)

​Specific