Question

What are the differences between undeclared and undefined variables in Javascript?

Answer 1

Below are the major differences between undeclared(not defined) and undefined variables,

undeclared	undefined
These variables do not exist in a program and are not declared	These variables declared in the program but have not assigned any value
If you try to read the value of an undeclared variable, then a runtime error is encountered	If you try to read the value of an undefined variable, an undefined value is returned.