Java script function tutorial

Function without parameter :

Below is the simple example for function without any parameter.

function welcomeMessage() {
  alert( 'Hello World!' );
}

welcomeMessage();

1. function is the keyword here

2. welcomeMessage is the function name.

3. welcomeMessage() is just calling the function.


So when you call control executes welcomeMessage() , it will call welcomeMessage function and executes the alert function inside that.

The below is little different because of variable declaration. See below,

let userName = 'Welcome';

function welcomeMessage() {
  let userName = "World"; // local variable

  let message = 'Hello, ' + userName;
  alert(message);
}

welcomeMessage();
alert( userName );

First It will show alert message like Hello World! Then after It will show Welcome. Because of variable declaration places and due to let keyword its happening.

Function with parameters :

We can also pass parameters to the function. See below example,

function welcomeMessage(msg1,msg2) {
  alert(msg1);

alert(msg2);
}

welcomeMessage("sample","Test");

Above we are passing two parameters and both were executed inside the function.

Function with returning a value :

The below we can see a function which is returning a value. Example below.

function sum(a, b) {
  return a + b;
}

let result = sum(1, 2);
alert( result ); // Output: 3

Here let result = sum(1,2) is the calling place and after executing the function , its returning value to result.

Conclusion :

These are the simple examples about function. Here the post we have used everywhere let keyword. We already saw let is a block level scope.