Hoisting and Temporal Dead Zone

JavaScript Hoisting

JavaScript goes through the code file collects references and stores those references in memory and executes code line-by-line.

The memory preparation phase is a hoisting, Take functions and store their reference, take let and const set uninitialized until get values and var set a undefined.

• function: functionReference

• let, const: uninitialized

• var: undefined

Case 1: Access fn before declaration.

No issue occurs when function call before declaration.

Case 2: Access var before declaration.

When you use var before their declaration error occurs as undefined.

Error:

No Error:

Case 3: Access let/const before declaration.

When you use let or const before their actual declaration, an error occurs as Reference error.

Error:

No Error:

Temporal Dead Zone

Zone before the actual declaration, Zone between variable use and its declaration is called TDZ.