syntax - Javascript variable declaration with brackets around initialized variables -

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• javascript object bracket notation ({ navigation } =) on left side of assign 4 answers

in react native website, there following line of code:

var react = require('react-native'); var { tabbarios, navigatorios } = react; 

in second line of example, meaning of brackets around tabbarios , navigatorios variables?

this called destructuring assignment. it's newer feature being brought in ecmascript 6 spec.

here example object:

var test = {   "hello": 1,   "world": 2 } 

if deconstruct this:

var {hello, world} = test; 

this equivalent doing:

var hello = test.hello,     world = test.world; 

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but, there more fun stuff can destructuring assignments...

lets have object:

var bucket = {   exampleobject: function(input){     this.input = input.trim();     return this.input;   },    testingobject: function(example){     this.example = example || {};     console.log(this.example.input);   } } 

just record, i've given members annoying names... when destructuring, can rename them this:

var {exampleobject: example, testingobject: test} = bucket; 

the binding pattern follows syntax so:

{objectmembername} // or {objectmembername: variablename} 

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for more information, can @ ecmascript 6 specification draft or mdn documentation