Everything in JavaScript happens inside an "Execution Context"

Execution Context

As soon as the JS program is run, the global execution context is created. It has 2 components, Memory & Code, so it is created in 2 phases.

Phase 1

Memory creation phase. In the memory creation phase, we allocate memory to all variables & functions inside global space. It allocates variables with the value of undefined & in functions, it just copies the whole code of the function.

Phase 2

Now all JS program is executed line by line it goes to the variable & replace it with the given value. & similarly, it will now invoke the function & goes to the next variable & it will invoke the function