Synchronous JavaScript :

Code runs line by line, and each line waits for the previous one to finish.

console . log ( " First " ); console . log ( " Second " ); console . log ( " Third " );

Output : First Second Third

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If a single line of code takes a long time (like a huge loop or a complex calculation), it blocks the rest of the program from running.

function slowTask (){ for ( let i = 1 ; i < 999999999 ; i ++ ){

} } console . log ( " First " ); slowTask (); console . log ( " Third " );

Output : First Third

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Asynchronous JavaScript :

Asynchronous code allows a program to start a long-running task and continue with others before that task finishes.

Code doesn't wait — it moves on and comes back when the task is done.So the page wouldn't freeze.

Used in:

Fetching data from an API.

Reading a file

Database queries

Timers

console . log ( " First " ); setTimeout (() => { console .…