JavaScript Functions


JavaScript functions perform calculations, comparisons and actions and the result can be returned to the caller. The JavaScript language have lots of built-in functions that let you handle everything from expressions and special characters, to conversion of strings to numeric values.

Like in most other languages you can also create your own functions.

JS JavaScript - Write a JavaScript function


var x = 0.00000000001; // Some very small number to test against. 
 
// The test function for integers.
function integerCheck(a, b, c) {
   // The test itself.
   if ((a * a) == ((b * b) + (c * c)))
      return true;
 
   return false;
 
} // End of the integer checking function. 
 
// The test function for floating-point numbers. 
function floatCheck(a, b, c) {
   // Make the test number. 
   var delta = ((a * a) - ((b * b) + (c * c)));
 
   // The test requires the absolute value 
   delta = Math.abs(delta);
 
   // If the difference is less than x, then it's pretty close. 
   if (delta < x)
      return true;
 
   return false;
} // End of the floating-poing check function.

Learn more about JavaScript Statements

Arrow function syntax, =>, a simpler way to to specify anonymous functions.

JS JavaScript - Arrow function syntax

var animals = [
  'dog',
  'cat',
  'horse',
  'bird'
];
 
alert(animals.map(animals => animals.length)); Result: 3,3,5,4

A drawback with arrow function syntax is that only Microsoft Edge supports it.


Learn more about JavaScript Numbers Methods

In the following example, the default value of c is 10, and the default value of a is 20. The function will use 10 as the value of c unless the caller passes in a distinct value (or undefined) as the second argument. The function will use 20 as the value of a unless the caller passes in a distinct value (or undefined) as the third argument.


var a = 20;
 
function f(b, c = 10, d = a) {
   return b + c + d;
}
 
alert(f(3));
alert(f(3, 3));
alert(f(3, 3, 3));
 
Result: 33, 26, 9

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JavaScript is one of the 3 core language technologies of the World Wide Web that all web developers must learn:

1.      HTML to define the content of web pages.

2.      CSS to specify the layout of web pages.

3.      JavaScript to program the behavior of web pages.

JavaScript is a scripting or programming language that allows you to implement complex things on web pages. Every time a web page does more than just sit there and display static information for you to look at, displaying timely content updates, interactive maps, animated 2D/3D graphics, scrolling video jukeboxes, etc. − you can bet that JavaScript is probably involved.


The benefits of using JavaScript are:

1.      You can validate user input before sending the page off to the server. This saves server traffic, which means less load on your server.

2.      Immediate feedback to the visitors − They don't have to wait for a page reload to see if they have forgotten to enter something.

3.      Increased interactivity − You can create interfaces that react when the user hovers over them with a mouse or activates them via the keyboard.

4.      Richer interfaces − You can use JavaScript to include such items as drag-and-drop components and sliders to give a Rich Interface to your site visitors.


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