How JS works?

Everything in JS happens inside an Execution Context.

Execution Context:
Component where JS is executed. It has:
1.Memory or Variable Env
Here variables are stored as key: valuepair.
2.Code Env or Thread of execution
This is the place where code is executed one line at a time.
Note: JavaScript is a synchronous single-thread language.

1nd Phase: Memory creation phase

• Everything happens in a ‘Global’ execution context.
• In this phase, memory is allocated to all variables and function(s).

• For variable(s), key is the variable name itself and value is undefined (even if the variable is initialized). And, for
  function(s), key is the function name and value is body of the
  code.
  2nd Phase: Code Execution phase

• Code is traversed line by line and actual value of variables are assigned to them.

• A new ‘local’ execution context is created, when function
  ‘invocation’ is encountered. Again, two phase perform their role.