JavaScript was developed by Brendan Eich in 1995 and became an ECMA standard in 1997. JavaScript is now considered to be a principal vehicle for building strong Web applications. If you are attending an interview for a JavaScript position then these JavaScript Interview Questions may give you an indication of what to study before the interview.
What is JavaScript?
• It was created to give HTML pages interactivity.
• It is a scripting language (a lightweight programming language).
• Usually, it is placed straight into HTML pages and it is an interpreted language.
• Everyone can use JavaScript without a license.
JavaScript is a scripting language with a simple syntax. It will authenticate data before it is put forward to a server saving extra processing. JavaScript reveals the visitor’s browser and loads another page depending on the browser. It also creates cookies and can store and get information on the visitor’s computer.
Explain What Is JavaScript. List data types supported by JavaScript.
JavaScript is an object – concerned computer programming language used to design interactive effects within web browsers. It is first utilized by the Netscape browser that gives access to the HTML Document Object Model (DOM).
Data types supported by JavaScript are:
• Undefined.
• Null.
• Boolean.
• String.
• Symbol.
• Number.
• Object.
Explain Closures in JavaScript.
Closures are the grouping of lexical function and environment in which the function was declared. This permits JavaScript programmers to write effective, concise, more creative and sensitive codes. The closure will be a combination of all the local variables that were in scope when the closure was created.
JavaScript is a very function-adapted language which gives the user freedom to use functions.
Explain JavaScript Event Delegation Model.
When capturing and bubbling, event delegation allows functions to implement one single handler to many elements at one time. Event delegation allows you to add event listeners to a parent instead of specific nodes. The specific listener examines bubbled events to find a match on the child elements.
What Are Global Variables? – It is a variable which has global scope and it is evident through the program unless shadowed.
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Why Do Most Developers Circumvent Globals? – JavaScript developers avoid globals to avoid encounters between globals and locals. Also, Global dependent codes are difficult to test and maintain.
What Are JavaScript Types? – JavaScript is a freely-typed language. When variables are created no type, declarations are needed. JavaScript works out what the type should be.
What Is the Difference Between Undefined and Null? – The variable value without a value is undefined – not initialised. Setting their value to null clears the variables. It is possible to test for each using the three equal signs or two equal signs. The null value uses force which could have odd results.
What is JavaScript’s ‘This’ Keyword? – Depending on how a function is called ‘this’ keyword usually refers to the object that owns the method. Essentially, it indicates the present in scope object that owns where you are in the code. In a Web Page, it indicates the Window object. JavaScript’s ‘this’ keyword will point to the object that created the event.
What is Event Bubbling? – This describes the performance of events in parent and child nodes in the Document Object Model (DOM). Parent nodes receive child node events. The advantage of this method is speed as the code only has to cross the DOM once. This will allow you to put more than a single event hearer on a DOM element as you can put one listener on all the components. This means code reduction and simplicity.
Explain JavaScript on your webpage.
HTML on the webpage identifies the content, and the appearance is identified using Cascading Style Sheets (CSS). The use of these two languages will design available static web pages regardless of the device which accesses the page.
However, the Web pages will need the visitor to fill out the form and wait for a new page to load. JavaScript solves this issue by transforming the static page into a page that interacts with your visitors. After a request, they will not need to wait for a new page to load. You should understand HTML and CSS which gives the formatting engine behind it.
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