JavaScript Hoisting

JavaScript Hoisting

Hoisting in JavaScript is a behavior in which a function or a variable can be used before declaration.


2 min read

Hoisting in JavaScript is a behaviour in which a function or a variable can be used before declaration. In Hoisting, though it seems that the declaration has moved up in the program, the actual thing is that the function and variable declarations are added to memory during the compile phase.

Variable Hoisting

In terms of variables and constants, the keyword var is hoisted. And let and const do not allow hoisting.

However, in JavaScript, initializations are not hoisted. Only declarations are moved to the memory in the compile phase. Due to that variables holds special value undefined.

In Hoisting, the variable declaration is only accessible to the immediate scope. If a variable is used with the let and const the keyword that variable is not hoisted.

Function Hoisting

A Function can be called before declaring it. However, when a function is used as an expression, an error occurs because only declarations are hoisted.

Generally, Hoisting is not performed in programming languages like C, C++, and Java. Hoisting can cause undesirable outcomes in your program. It is best to declare variables and functions first before using them and avoid hoisting.

In the case of variables, it is better to use let than var.

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