javascript - What's the synax `async/await` in zombiejs code? -

when read source code of zombie.js, found async/await keyword:

before(async function() {   await browser.visit('/streaming');   await browser.pressbutton('1'); }); 

https://github.com/assaf/zombie/blob/41807a39c7aa1a13c4ef51575e0d581be96175bc/test/event_source_test.js#l60

why can use such keywords? behaviour of code? tried find clue codebase, not lucky

if check out gulpfile used build project, can see source piped through babel.

gulp.task('build', ['clean'], function() {   return gulp     .src('src/**/*.js')     .pipe(sourcemaps.init())     .pipe(babel({       experimental: true,       loose:        'all',       optional:     [         'bluebirdcoroutines',         'runtime'       ]     })) }); 

babel transpiler allows write es6+ code , transpile es5.

babel turn es6+ code es5 friendly code, can start using right without waiting browser support.

if check out docs on babel's site, can see in es7 section of experimental section, there implementation asyncfunctions.

these keywords part of es7 specification, haven't stabilised. hence them being included experimental features of babel.

in simplified terms, async function allow await call returns promise.

async function() {   // flow suspended here until   // promise returned somefunction resolved   await somefunction() } 

es6 include known generators, similar thing, aren't specific promises. might start seeing yield keyword around, or functions declared function* () {}. what's known generator functions.

there particularly good article pouchdb explains real world use case these features.