Javascript has two types of scopes global and local(function) level scope. Variables declared globally that are visible throughout the javascript program come under global scope. Variables declared inside functions, may have same name as global varibles, are accessible only within that function are local variables.
1) No block level scope(except a special case – Block-scoped variables)
2) Variables are hoisted (variables declaration are moved to top and then run)
3) Chaining of scopes. Any function defined within another function has a local scope which is linked to the outer function.
Also any property assigned to window object is also treated as global variable.
If variables are defined without var(no var) outside functions, they are treated as global variable. “no var” variable definition inside function will look up the scope chain until it finds the variable or hits the global scope (at which point it will create it).