Declaration Notation in JavaScript

There is a slightly shorter way to create a function binding. When the function keyword is used at the start of a statement, it works differently.

function square(x) {

return x * x;


This is a function declaration. The statement defines the binding square and points it at the given function. It is slightly easier to write and doesn’t require a semicolon after the function.

There is one subtlety with this form of function definition.

console.log(“The future says:”, future());

function future() {

return “You’ll never have flying cars”;


The preceding code works, even though the function is defined below the code that uses it. Function declarations are not part of the regular top- to-bottom flow of control. They are conceptually moved to the top of their scope and can be used by all the code in that scope. This is sometimes useful because it offers the freedom to order code in a way that seems meaningful, without worrying about having to define all functions before they are used.

Source: Haverbeke Marijn (2018), Eloquent JavaScript: A Modern Introduction to Programming,

No Starch Press; 3rd edition.

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