What happens when JavaScript variable name and function name is the same?
Functions are a type of object which are a type of value.
Values can be stored in variables (and properties, and passed as arguments to functions, etc).
A function declaration:
- Creates a named function
- Creates a variable in the current scope with the same name as the function (unless such a variable already exists)
- Assigns the function to that variable
- Is hoisted
A var
statement:
- Creates a variable in the current scope with the specified name (unless such a variable already exists)
- Is hoisted
- Doesn't assign a value to that variable (unless combined with an assignment operator)
Both your declaration and var
statement are hoisted. Only one of them assigns a value to the variable a
.
In JavaScript both function declaration and variable declarations are hoisted to the top of the function, if defined in a function, or the top of the global context, if outside a function. And function declaration takes precedence over variable declarations (but not over variable assignment).
Function Declaration Overrides Variable Declaration When Hoisted
First you declare a variable:
var a; // value of a is undefined
Second, the value of a
is a function because function declaration takes precedence over variable declarations (but not over variable assignment):
function a(x) {
return x * 2;
}
And that is what you get when you call alert(a);
.
But, if instead of declaring a variable you make variable assignment: var a = 4;
then the assigned value 4
will prevail.