JavaScript Functions

Internal

• JavaScript Concepts

Overview

function name(parameter1, parameter2, parameter3) {
  // code to be executed
}

Function Parameters and Arguments

The names listed in the function definition are the function parameters. The values passed to the function are the function arguments.

A JavaScript function does not specify data types for its parameters, it does not perform type checking on its arguments and it does not check the number of arguments received.

Missing Argument

If a function is called with missing arguments, the corresponding argument values are set to undefined.

function test(a, b) {
    console.log(a);
    console.log(b);
}
test('something');
something
undefined

Default Paramenter Value

ECMAScript 2015 allows default parameter values in the function declaration:

function test(a, b = 2) {
  // ...
}

The arguments Object

A function has a built-in object called the arguments object. The arguments object contains an array of the arguments used when the function was invoked:

function test() {
  var i;
  for(i = 0; i < arguments.length; i ++) {
    console.log(arguments[i]);
  }
}
test(1, 2, 3, 20, 50);

Declaration

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/function

Function Expressions

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/function