JS: function (keyword)

By Xah Lee. Date: . Last updated: .

Create a Function

There are 3 ways to create a function.

The most common way is by the keyword function.

Another common way is by Arrow Function. this is shorter, and simpler.

Another way is by Function Constructor. this is rarely used. only for creating functions at runtime.

Keyword “function”

Function declaration

The syntax is:

function name (parameters) {body_statements}

function ff(x) {
 return x + 1;
}

console.log(ff(2));
// 3
// 2 parameters
function ff(x, y) {
 return x + y;
}

console.log(ff(3, 4));
// 7

Return Statement

In the function body, you can have 0 or more return expr.

When program reaches the return statement, it'll exit the function, and return the value.

Function without return statement returns the value undefined.

Function expression

the function keyword can be assigned to a variable. when doing so, it is called a function expression.

const ff = function (x) {
 return "Hello " + x;
};
console.log(ff("Alice"));
// Hello Alice