ECMA Script Interview Questions & Answers

ECMAScript, also known as JavaScript, is a programming language adopted by the European Computer Manufacturer’s Association as a standard for performing computations in Web applications. ECMAScript is the official client-side scripting language of VoiceXML. ECMAScript is a limited programming model for simple data manipulation ECMAScript is object-oriented and is considered as a core programming language. It has also become of the most widely used general purpose programming languages. Additionally, it is widely used for embedded and server programming applications but can also be used for any application which needs scripting language.

JavaScript is a scripting language most often used for client-side web development. It was the originating dialect of the ECMAScript standard. ECMAScript and Live Script are other names for JavaScript. The current JavaScript that is supported in browsers is ECMAScript

Babel is the one of the most popular JavaScript transpiler and becomes the industry standard. It allows us to write ES6 code and convert it back in pre-Es6 JavaScript that browser supports.

A promise is an object that may produce a single value sometime in the future: either a resolved value, or a reason that it’s not resolved (a network error occurred). A promise may be in one of 3 possible states (fulfilled, rejected, or pending). Promise users can attach callbacks to handle the fulfilled value or the reason for rejection.

Webpack allow you to run an environment that hosts babel. Webpack is open source JavaScript module bundler which takes modules with dependencies and generates static assets representing those modules.

Traceur is a JavaScript. Next-to-JavaScript-of-today compiler that allows you to use features from the future today. Traceur supports ES6 as well as some experimental ES.next features.Traceur’s goal is to inform the design of new JavaScript features which are only valuable if they allow you to write better code. Traceur allows you to try out new and proposed language features today, helping you say what you mean in your code while informing the standards process. JavaScript’s evolution needs your input.

Reflect is a built-in object that provides methods for intercept able JavaScript operations. The methods are the same as those of proxy handlers. Reflect is not a function object, so it’s not constructible. Full reflection API exposing the runtime-level meta-operations on objects. This is effectively the inverse of the Proxy API, and allows making calls corresponding to the same meta-operations as the proxy traps. Especially useful for implementing proxies.

Template literals are the string with embedded code and variables inside. Template literal allows concatenation and interpolation in much more comprehensive and clear in comparison with prior versions of Ecma script.

Destructuring allows binding using pattern matching, with support for matching arrays and objects. Destructuring is fail-soft, similar to standard object lookup foo [“bar”], producing undefined values when not found.

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();

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”, 42)

hash.set (1, 34);

console.log (hash); //Map {“hello” => 42, 1 => 34}

BabelJS is the most popular transpiler that transforms new JavaScript ES6 to Old JavaScript ES5.BabelJS makes it possible for writing the next generation of JavaScript today (means ES2017).BabelJS simply takes ES2015 file and transform it into ES5 file. Current browsers versions can now understand the new JavaScript code (ES2017), even if they don’t yet support it.

List some new features of E6

• Support for constants (immutable variables)
• Block-Scope support for both variables, contants, functions, Arrow Functions
• Extended Parameter Handling
• Template Literals and Extended Literals
• Enhanced Regular Expression and Enhanced Object Properties
• Destructuring Assignment
• Modules, Classes, Iterators, Generators
• Support for Map/Set & WeakMap/WeakSet
• Promises, Meta-Programming, Internationalization & Localization

ECMAScript 7 is the next evolution of the ECMA-262 standard. Some features are

• Exponentiation Operator
• Array comprehensions and Generator comprehensions
• Async functions and Async generators
• Object Observe and Typed Objects
• Object.getOwnPropertyDescriptors
• Array.prototype.includes

ES8 also called ES2017

• Object. Values ​​and Object. Entries
• Object.getOwnPropertyDescriptors
• Superfluous commas in the list of function parameters and calling
• Asynchronous Functions, await
• Paddy String
• SharedArrayBuffer

ES9-2018 Edition-ECMAScript 2018

• Rest/Spread Properties
• Asynchronous iterator
• Promise,prototype,finally
• Object expansion operator
• Template string for non escape sequence

And New RegEXp

• Unicode escape
• s/dotAll mode
• Named capture group
• Lookbehind assertions

ES10-2019 Edition-ECMAScript 2019

• prototype.(flat, flatmap)
• prototype.(trimStart,trimEnd, matchAll*)
• fromEntries
• prototype.toString
• prototype.description
• Optional catch binding
• JSON superset
• Improvement on Unicode support for JSON.stringify()
• sort now retains order if keys are equal
• BigInt
• globalThis