JavaScript Interview Questions and Answers
JavaScript is a high-level programming language that is known for its dynamic, prototype-based and weakly typed characteristics. It conforms to the ECMAScript specification and is one of the core technologies of the World Wide Web. Initially only implemented client-side, JavaScript is now embedded in other types of software, including server-side in web servers and non-web programs such as PDF software and word processors. This information is often asked in JavaScript interview questions.
JS Interview Questions
| undefined | Not defined | |
|---|---|---|
| 1. | A variable was declared with a keyword "var" but not assigned with a value. | A variable have not been declared without assignment: |
| 2. | Example :var a = 1, b; |
Example :var a = 1, b; |
It is not a jQuery feature but a feature for debugging purposes used by developers. It is used to writes a message to the console.
console.log() accepts a parameter which can be an object, an array or any message.
Syntax : console.log(name); // here name is object, an array or variable.
$('#form').submit(function() {
console.log(‘Your form is submitted successfully!’);
// do something
});
| S.no | Call() | Apply() |
|---|---|---|
| 1. | In JavaScript, call() is a predefined method used to invoke (call) methods with the use of an owner object as an argument (parameter). | apply() is a method to write another way which can be used on different objects. It’s usually action similar to call() action. |
Singleton is a JavaScript object which can be instantiated one time, whereas the singleton pattern is a design pattern that restricts the reinstallation of a class to one object. It allows only a single instance of itself to be created and can give access to that created instance.
Point to be noted:- Don’t let this JavaScript Interview Question take your job opportunity. Read it twice and then go for the interview.
It’s an advance object-oriented solution designed to solve commonly occurring software problems. These are reusable designs and interact with objects.
typeof
Example
var x = 12345;
console.log(typeof x)
x = 'string';
console.log(typeof x)
x = { key: 'value' };
console.log(typeof x)
Answer
number
string
object
if (Math.round(null) > 0.5) {
var x = 1;
} else {
var x = 2;
}
console.log(x);
2
const x = [];
x = 5;
console.log(x);
It will give an error like "TypeError: Assignment to constant variable".
On the basis of functioning
JavaScript is a scripting language which is compatible with all the major browsers and used to create interactive web-based applications. While jQuery is a framework which is the fastest JavaScript library used for the simplification of HTML document.
Time and simplicity
JavaScript is complex because it consumes the time of developers as it is important for the developers if they are using JavaScript then they have to create their own script. In the case of jQuery, developers need not write scripting as it already exists in the libraries.
Animation support
With JavaScript, it cannot be possible for the developer to use animation. On the other hand, jQuery allows the developers to use unbuild animations to make the applications interactive and attractive.
Featural aspects
JavaScript programming language is a combination of the European Manufacturing Association Script (ECMA) and Document Object Model (DOM). While on the other hand jQuery has a Document Object Model (DOM).
Interactivity feature
With the use of JavaScript, developers can make web pages more useful by suppling immediate feedback. While in case of jQuery developer can create web-based applications which becomes easier for the developer to customize the application as per the user's requirement.
Development History of JavaScript
Invented by Brendan Eich in 1995, JavaScript became an ECMA standard in 1997. JavaScript was first to run on the Netscape 2 browser.
Latest Version: ECMAScript 2018 or ES9 is the latest version and was released in October 2018.
Advantages of JavaScript
- Client-side JavaScript is quite fast.
- The syntax is simple and flexible.
- It develops well with most of the other popular languages.
- Drag and drop components give a rich interface to your site.
- Third party add-ons enable developers to write rich snippets.