CHAPTER 6
Functions
A function is a self-contained collection of statements that run as a single unit: essen‐
tially, you can think of it as a subprogram. Functions are central to JavaScript’s power
and expressiveness, and this chapter introduces you to their basic usage and
mechanics.
Every function has a body; this is the collection of statements that compose the
function:
function
sayHello
() {
// this is the body; it started with an opening curly brace...
console
.
log
(
"Hello world!"
);
console
.
log
(
"¡Hola mundo!"
);
console
.
log
(
"Hallo wereld!"
);
console
.
log
(
"Привет мир!"
);
// ...and ends with a closing curly brace
}
This is an example of a function declaration: we’re declaring a function called
say
Hello
. Simply declaring a function does not execute the body: if you try this example,
you will not see our multilingual “Hello, World” messages printed to the console. To
call a function (also called running, executing, invoking, or dispatching), you use the
name of the function followed by parentheses:
sayHello
();
// "Hello, World!" printed to the
// console in different languages
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