Functions

Function is a code block that executes certain task.

Syntax

function funcName(args) { // Code to execute. }

Void Example

A void function doesn't return any value.

Example:

printHi(); // Calling a function: function printHi() { console.log("Hi!"); }

Output:

Hi!

Returning Result

Via the return keyword a result can be returned.

Let's have an example in which rectangle's area is calculated by passing arguments about it's sides.

Example:

let area = calcRectangleArea(3, 4); console.log(area); function calcRectangleArea(widthArg, heightArg) { return widthArg * heightArg; }

Output:

12

There are couple of things to mark:

• A functions is defined at lines 4 - 6. It accepts two arguments - widthArg and heightArg.
• The function calcRectangleArea returns a result.
• calcRectangleArea is called at line 1.
• It's returned value is set in the variable area.

Not passing argument

If arguments is not passed it's value is considered undefined.

printArgs(3, 4); function printArgs(a, b, c) { console.log(a); console.log(b); console.log(c); }

Output:

3 4 undefined

The function printArgs expects 3 arguments but the last one (c) is not passed. For that reason c has undefined value.

Default Value

Default value may be specified for function parameters.

Let's look at the following:

printArg(5); printArg(); function printArg(arg = 3) { console.log(arg); }

Output:

5 3

At line 2 the function argument is not passed thus it takes the default value - 3 specified at line 4.