Undefined value primitive value is used when a variable has not been assigned a value.

The standard clearly defines that you will receive undefined when accessing uninitialized variables, non-existing object properties, non-existing array elements, and alike.

let movie = { name: 'Nobody' };
movie.year; // => undefined

Undefined type is a type whose sole value is the undefined value.

A declared variable but not yet assigned with a value (uninitialized) is by default undefined.

Favor const, otherwise use let, but say goodbye to var

const and let are block scoped (contrary to older function scoped var) and exist in a…

React is a JavaScript “library”. It is not exactly a “framework”. It is not a complete solution and you will often need to use more libraries with React to form any solution. React does not assume anything about the other parts in any solution.


DOM is the “Document Object Model”. It’s the browsers’ programming interface for HTML (and XML) documents that treats them as tree structures. The DOM API can be used to change a document's structure, style, and content.

JavaScript was created in 1995 by Brendan Eich while he was an engineer at Netscape. JavaScript was first released with Netscape 2 early in 1996. It was originally going to be called LiveScript, but it was renamed in an ill-fated marketing decision that attempted to capitalize on the popularity of Sun Microsystem’s Java language — despite the two having very little in common.

Unlike most programming languages, the JavaScript language has no concept of input or output. …

Extra “s” means your connection to that website is secure and encrypted; any data you enter is safely shared with that website. The technology that powers that little “s” is called SSL, which stands for “Secure Sockets Layer.”

As a consumer, you always want to see https:// when visiting any site you trust with your essential information. As a marketer, you’ll want to make sure you have an SSL or two for your audience.

What is an SSL certificate?

SSL certificates are small data files that cryptographically establish an encrypted link between a web server and a browser. …

What is a Number?

The Number type is a double-precision 64-bit binary format IEEE 754 value (numbers between -(253 − 1) and 253 − 1). But because such Number values aren’t real integers, you have to be a little careful.
ECMAScript has two built-in numeric types: Number and BigInt.
See some examples:

console.log(5 / 2);             // 2.5, not 2
console.log(Math.floor(5 / 2)); // 2

The standard arithmetic operators are supported, including addition, subtraction, modulus (or remainder) arithmetic, and so forth. There’s also a built-in object that we did not mention earlier called Math that provides advanced mathematical functions and constants:


You can convert…

Pulok Chowdhury

Programmer | Developer | Dreamer

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