2
A so-called “immediately invoked function expression” (IIFE), which we will cover in
This is a common technique, and you will see
this
get assigned to
self
or
that
.
Arrow functions, which we’ll see later in this chapter, are another way of addressing
this problem.
Function Expressions and Anonymous Functions
So far, we’ve been dealing exclusively with function declarations, which give functions
both a body (which defines what the function does) and an identifier (so we can call it
later). JavaScript also supports anonymous functions, which don’t necessarily have an
identifier.
You might reasonably be wondering what use is a function without an identifier.
Without an identifier, how are we to call it? The answer lies in understanding function
expressions. We know that an expression is something that evaluates to a value, and
we also know that functions are values like any other in JavaScript. A function expres‐
sion is simply a way to declare a (possibly unnamed) function. A function expression
can be assigned to something (thereby giving it an identifier), or called immediately.
Function expressions are syntactically identical to function declarations except that
you can omit the function name. Let’s consider the example where we use a function
expression and assign the result to a variable (which is effectively equivalent to a
function declaration):
const
f
=
function
() {
// ...
};
The outcome is the same as if we had declared the function in the usual way: we’re
left with an identifier
f
that refers to a function. Just as with regular function declara‐
tion, we can call the function with
f()
. The only difference is that we are creating an
anonymous function (by using a function expression) and assigning it to a variable.
Anonymous functions are used all the time: as arguments to other functions or meth‐
ods, or to create function properties in an object. We will see these uses throughout
the book.
I said that the function name is optional in a function expression…so what happens
when we give the function a name and assign it to a variable (and why would we want
to do this)? For example:
const
g
=
function
f
() {
// ...
}
112 | Chapter 6: Functions
