Spread Operator and Destructuring

 ES6 introduces the spread operator, which allows to expand array and other expressions in places where multiple parameters or elements are expected.

ES5 code

        var arr = [6, 89, 3, 45];
        var maximus = Math.max.apply(null, arr);
        console.log(maximus)

89

ES6 code. (Math.max(arr) return NaN. spread operator makes this syntax much better to read and maintain.

        var arr = [6, 89, 3, 45];

        var maximus = Math.max(...arr);

        console.log(maximus)

89

Destructuring Assigment to Extract values from Objects

    Introduced Destructuring assigment in ES6. it Assign values taken directly from an object.

ES5 Code

 const user = { name: 'Shreyash Kolhe', age: 21 };
        const name = user.name;
        const age = user.age;

ES6 code

 const {name, age} = user;

Use Destructuring Assignement to Assign variables from objects.

    

        Desructuring allows you to assign a new variable name when extracting values. You can do this by putting the new name after a colon when assigning the value.

       const user = {name: 'shreyash', age: 21};
       console.log(user)

{name: 'shreyash', age: 21}

Here's how you can give new variable names in the assignement.

        const profile = {
            name : 'shreyash',
            age : 21
        }
       const { name: userName, age: userAge } = profile;
       console.log(userName)
       console.log(userAge)

shreyash
21

Destructuring Assignement to Assign Variable from nested Objects.

const profile = {
    fy : {name:'shreyash', age:19},
    sy : {name : 'vaibhav', age:20},
    ty : {name : 'changu', age: 21}
};
const {sy : { name: newName, age: newAge}} = profile;

Destructuring Arrays.

ES6 makes destructuring arrays is easy like destructuring objects. 

// array Destructuring 
const [a, b] = [1,2];
console.log(a, b)

1 2

// array rest parameter destructuring 
const [a1,b1, ...arr] = [1,2,3,4,5];
console.log(a1,b1)
console.log(arr)

1 2
[ 3, 4, 5 ]

Destructuring Assignment to pass an objects as a function's parameters.

const markes = {
    nodejs: 89,
    angular: 80,
    reactJs: 99
}
const total = ({ nodejs, angular, reactJs }) => (nodejs + angular + reactJs)/3;
console.log (markes)
console.log(total(markes))

{ nodejs: 89, angular: 80, reactJs: 99 }
89.33333333333333