Function
A function name is an identifier included as part of a function declaration or function expression. The function name's scope depends on whether the function name is a declaration or expression.
Different types of functions
An anonymous function is a function without a function name. Only function expressions can be anonymous, function declarations must have a name:
// Anonymous function created as a function expression
(
function
(
)
{
}
)
;
// Anonymous function created as an arrow function
(
)
=>
{
}
;
The following terms are not used in the ECMAScript language specification, they're jargon used to refer to different types of functions.
A named function is a function with a function name:
// Function declaration
function
foo
(
)
{
}
// Named function expression
(
function
bar
(
)
{
}
)
;
// Arrow function
const
baz
=
(
)
=>
{
}
;
An inner function
is a function inside another function (square
in this case). An outer function
is a function containing a function (addSquares
in this case):
function
addSquares
(
a,
b
)
{
function
square
(
x
)
{
return
x *
x;
}
return
square
(
a)
+
square
(
b)
;
}
// Arrow function
const
addSquares2
=
(
a,
b
)
=>
{
const
square
=
(
x
)
=>
x *
x;
return
square
(
a)
+
square
(
b)
;
}
;
A recursive function is a function that calls itself. See recursion .
function
loop
(
x
)
{
if
(
x >=
10
)
return
;
loop
(
x +
1
)
;
}
// Arrow function
const
loop2
=
(
x
)
=>
{
if
(
x >=
10
)
return
;
loop
(
x +
1
)
;
}
;
An Immediately Invoked Function Expression (IIFE ) is a function that is called directly after the function is loaded into the browser's compiler. The way to identify an IIFE is by locating the extra left and right parenthesis at the end of the function's definition.
Function expressions, named or anonymous, can be called immediately.
(
function
foo
(
)
{
console.
log
(
"Hello Foo"
)
;
}
)
(
)
;
(
function
food
(
)
{
console.
log
(
"Hello Food"
)
;
}
)
(
)
;
(
(
)
=>
console.
log
(
"hello world"
)
)
(
)
;
Declared functions can't be called immediately this way, because IIFEs must be function expressions .
function
foo
(
)
{
console.
log
(
'Hello Foo'
)
;
}
(
)
;
If you'd like to know more about IIFEs, check out the following page on Wikipedia: Immediately Invoked Function Expression