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Eloquent JavaScript

Cover of Eloquent JavaScript by Marijn Haverbeke Published by No Starch Press

Chapter 2. Functions

We have already used several functions in the previous chapter—things such as alert and print—to order the machine to perform a specific operation. In this chapter, we will start creating our own functions, making it possible to extend the vocabulary that we have available. In a way, this resembles defining our own words inside a story we are writing to increase our expressiveness. Although such a thing is considered rather bad style in prose, in programming it is indispensable.

The Anatomy of a Function Definition

In its most basic form, a function definition looks like this:

function square(x) {
  return x * x;

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Here, square is the name of the function. x is the name of its (first and only) argument. return ...

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