Javascript Function

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Functions allow the encapsulation of statements.

Functions in Javascript are declared using the function keyword, followed by arguments and the function body.

The basic syntax is as follows:

function functionName(arg0, arg1,...,argN) {
    statements
}

Example

Here's an example. This function is called using its name, followed by the function arguments enclosed in parentheses and separated by commas in case of multiple arguments.

function sayHi(name, message) {
    console.log("Hello " + name + ", " + message);
}
sayHi("Javascript", "is it working?");

The code above generates the following result.

function return

Functions can return a value using the return statement followed by the value to return.

function return Example 1

function sum(num1, num2) {
   return num1 + num2;
}
var result = sum(5, 10);
console.log(result);

The code above generates the following result.

A function stops executing and exits immediately when it encounters the return statement. Therefore, any code after a return statement will never be executed. For example:

function sum(num1, num2) {
   return num1 + num2;
   console.log("Hello world");    //never executed
}
var result = sum(5, 10);
console.log(result);

The code above generates the following result.

function return Example 2

It's also possible to have more than one return statement in a function, like this:

function diff(num1, num2) {
   if (num1 < num2) {
       return num2 - num1;
   } else {
       return num1 - num2;
   }
}
var result = diff(5, 10);
console.log(result);

The code above generates the following result.

function return Example 3

The return statement can be used without return value, and will return undefined.

function sayHi(name, message) {
   return;
   console.log("Hello " + name + ", " + message);    //never called
}
var result = sayHi(5, 10);
console.log(result);

The code above generates the following result.

Note for function return

Strict mode places several restrictions on functions:

• No function can be named eval or arguments.
• No named parameter can be named eval or arguments.
• No two named parameters can have the same name.

Recursive function

A recursive function is a function which calls itself by name.

arguments.callee is a pointer to the function being executed and, as such, can be used to call the function recursively

function factorial(num){
   if (num <= 1){
      return 1;
   } else {
      return num * arguments.callee(num-1);
   }
}

Strict Mode for Recursive function

The value of arguments.callee is not accessible to a script running in strict mode. In strict mode, you can use named function expressions to define recursive functions

var factorial = (function f(num){
   if (num <= 1){
      return 1;
   } else {
      return num * f(num-1);
   }
});

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