In JavaScript, both of these operators are comparison operators. While the “==” operator is used for comparing values, the “===” operator is used to compare values and types.

In JavaScript, the “var” keyword is used from the beginning, while the “let” keyword was added much later in 2015. The “var” keyword holds a function scope. The variable you specify anywhere in the function using “var” is accessible. On the other hand, a variable scope declared with the “let” keyword is limited to the block where it is declared.

JavaScript is a dynamically typed programming language for building web applications. Here, developers check the type of a variable during run-time. On the other hand, the type of a variable in a statically typed language is checked during compile-time. Being a dynamically typed language, the variables in JavaScript are not related to any type, making them hold values of any data type.

The strict mode is a new feature launched in ECMAScript 5 that allows developers to write a function or a code in a strict operational environment. Mostly, the programming language is not too “severe” with regard to throwing errors. However, in the strict mode, all error forms (including silent errors) are thrown. This makes debugging a lot simpler for developers.

Here are some of the most important characteristics of the strict mode in JavaScript:

In JavaScript, self-invoking functions are the functions where self-invoking expressions are automatically invoked without being requested. A function expression will execute automatically if it is followed by (). It is also important to note that a function declaration is not capable of being invoked by itself.

Generally, a JavaScript developer declares and calls a function. However, they may use anonymous functions to automatically run a function when it is described. It is not called again and these functions have no names.

In JavaScript, the prototype design pattern is used to produce different objects. Instead of returning uninitialized objects, the design pattern creates objects with values replicated from a template - or sample - object.

A good example of prototype patterns in JavaScript coming in handy is the introduction of business objects with parameters. Here, the new business object’s default settings are stored in the concerned prototype object. The prototype design pattern is rarely used in traditional programming languages. However, it is used to create new objects and templates in JavaScript as it is a prototypical language.

Here are the different methods used to declare or construct a JavaScript object:

In JavaScript, promises are used by developers to handle asynchronous operations. Before the introduction of promises, developers used callbacks for this function. However, the limited functionality of callbacks often led to unmanageable code if multiple callbacks are used..

A JavaScript promise has four different states: