ES6 Interview Questions and Answers (JavaScript)

ES6 stands for ECMAScript version 6. It is a Client-side scripting language. Now,10th edition ECMAScript 2019, was published in June 2019.

Read More: Intr0duction to ECMAScript (ES)

• Support for constants
• Arrow functions
• Object Literals
• Promises in Es6
• Support Map/set
• Default parameters
• Rest and Spread operators
• Objects, Modules, classes, iterators, and generators in ES6
• Destructing Assignment

The WeakMap is same as Map where it is a collection of key/value pairs. But in WeakMap, the keys must be objects and the values can be arbitrary values.

The WeakSet object lets you store weakly held objects in a collection.

Navigator-specific methods are:

• javaEnabled()
• taintEnabled()
• refresh
• preference(name,value)

pop() method is used to remove the last element from an array and returns that element.

• isNaN() :Determines whether the passed value is NaN.
• isFinite() : Determines whether the passed value is a finite number.
• isInteger() :Determines whether the passed value is an integer.
• isSafeInteger() :Determines whether the passed value is a safe integer (number between -(253 – 1) and 253- 1)
• parseFloat() :The value is the same as parseFloat() of the global object
• parseInt() :The value is the same as parseInt() of the global object

By using export default element_name

By using export {element_name1,element_name2,….}

It is the replace() method of window.location object which is used to replace the current document with a new one.

It is used to send a warning message to the users and provides only one button “OK” to select and proceed.

An iterator accesses the items from a collection one at a time, while keeping track of its current position within that sequence. It provides a next () method which returns the next item in the sequence. This method returns an object with two properties: done and value

• EvalError: regarding the global function eval().
• RangeError :when a numeric variable or parameter is outside of its valid range.
• ReferenceError :when dereferencing an invalid reference.
• SyntaxError : while parsing the code.
• TypeError : when a variable or parameter is not of a valid type.
• URIError : when encodeURI() or decodeURI() are passed invalid parameters.

In Es6 you can create a class using the Class keyword.Below is sample javascript class in ES6.

class User{

    constructor(name,age) {

        this.name  = name;

        this.age = age;

    }

    getData() {

        console.log(this.name + " is " + this.age + " years old !");

    }

}

var user = new User("foo", 7);

s1.getData();

It provides a new way to manipulate array and objects in Es6.A Spread operator is represented by … followed by the variable name.Check below Example:

let a =[6,7,8,9];

let b=[1,2,3,...a,10];

console.log(b);

output:  // [1,2,3,6,7,8,9,10]

The Map object is a simple key/value map. Any value (both objects and primitive values) may be used as either a key or a value. Syntax [key, value]. e.g.

hash = new Map ()

hash.set ("hello", 44)

hash.set (1, 38);

console.log (hash); //Map {"hello" => 44, 1 => 38}