JavaScript: Topics To Know

Truthy & Falsy Value:

Truthy:

A value that is considered true when encountered in a Boolean context is called truthy value. All values are truthy unless they are defined as falsy (i.e., except for false, 0, -0, "", null, undefined, and NaN).

Falsy: A value that is considered false when encountered in a Boolean context is called falsy value. Any value which is explicitly false, 0, -0, "", null, undefined, and NaN

Null Vs. Undefined:

You may think, null and undefined are same, but it’s not. Let’s explore the difference between them.

null: null has two important features:

• null is an empty or non-existent value.
• null must be assigned.

undefined: Undefined most typically means a variable has been declared, but not defined. Example:

let b;

console.log(b);

DOM: The elaboration of DOM is Document Object Model. DOM is bassically a platform or programming interface that allows programs and scripts to dynamically access and update the content, structure, and style of a document.

Every Element in a document is part of the document object model.

“this” keyword:

In JavavaScript this keyword is used to refer something indirectly to the object in context.

Example:

Here, this refers to object in context which is person.

Synchronous Operations:

Normally, JavaScript operations are synchronous and execute the code from top to bottom. And it means, every step in an operation waits for the previous step to execute completely.

Example:

Asynchronous Operations:

Usually, JavaScript shows blocking behavior, i.e. if you write a code where a while loop is executed for 3 seconds, in that case, in the meantime the browser will block everything. And after 3 seconds it will run the next command. This is where asynchronous operation comes. In case of this kind of operation, it does not block anything. We can think of a setTimeOut() function in this regard.

Example: