Javascript object bracket notation ({ Navigation } =) on left side of assign
JavascriptWebpackEcmascript 6Javascript Problem Overview
I haven't seen this syntax before and am wondering what it's all about.
var { Navigation } = require('react-router');
The brackets on the left are throwing a syntax error:
> unexpected token {
I'm not sure what part of the webpack config is transforming or what the purpose of the syntax is. Is it a Harmony thing? Can someone enlighten me?
Javascript Solutions
Solution 1 - Javascript
It's called destructuring assignment and it's part of the ES2015 standard.
> The destructuring assignment syntax is a JavaScript expression that > makes it possible to extract data from arrays or objects using a > syntax that mirrors the construction of array and object literals. > > Source: Destructuring assignment reference on MDN
Object destructuring
var o = {p: 42, q: true};
var {p, q} = o;
console.log(p); // 42
console.log(q); // true
// Assign new variable names
var {p: foo, q: bar} = o;
console.log(foo); // 42
console.log(bar); // true
Array destructuring
var foo = ["one", "two", "three"];
// without destructuring
var one = foo[0];
var two = foo[1];
var three = foo[2];
// with destructuring
var [one, two, three] = foo;
Solution 2 - Javascript
This is destructuring assignment. It's a new feature of ECMAScript 2015.
var {
AppRegistry,
StyleSheet,
Text,
View,
} = React;
Is the equivalent to:
var AppRegistry = React.AppRegistry;
var StyleSheet = React.StyleSheet;
var Text = React.Text;
var View = React.View;
Solution 3 - Javascript
var { Navigation } = require('react-router');
... uses destructuring to achieve the same thing as ...
var Navigation = require('react-router').Navigation;
... but is far more readable.
Solution 4 - Javascript
It's a new feature in ES6 to destructure objects.
As we all know that there is an assignment operation taking place here, which means right side value is getting assigned to left side variable.
var { Navigation } = require('react-router');
In this case require('react-router')
method returns an object with key-value pair, something like:
{ Navigation: function a(){},
Example1: function b(){},
Example2: function c(){}
}
And if we would like to take one key in that returned object say Navigation
to a variable we can use Object destructuring for that.
This will only be possible only if we have the key in hand.
So after the assignment statement, local variable Navigation
will contain function a(){}
Another example looks like this.
var { p, q } = { p: 1, q:2, r:3, s:4 };
console.log(p) //1;
console.log(q) //2;
Solution 5 - Javascript
instead of
const salary = personnel.salary
const sex = personnel.sex
const age = personnel.age
simply
const {salary, age, sex} = personnel