Voice of a Developer: Part Ten - JavaScript Functions

Introduction

JavaScript is the language of the Web. This series of articles will talk about my observations learned during my decade of software development experience with JavaScript.

Before moving further let us look at the previous articles of the series:

In JavaScript, functions are the 1st class citizens of language. These are the bread and butter of JavaScript. Go in deep now:

Functions in-depth

Function keyword, followed by a name, followed by parentheses (). You can get function definition or invoke the function, ex:

function myFunction(a, b) {
return a * b; // Function returns the multiplication of a and b
}

The () invokes the function,

Properties of function

Let us dive into some properties of the function, ex-

Call v/s Apply

If you want to assign the value of a function we use straight forward way, i.e.,

var val = myFunction (2,3); // val = 6

There are two other way to achieve it using call or apply property,

var val = 0;
myFunction.apply(val, [2, 3]); // 6 as output
myFunction.call(val, 2, 3); // 6 as output

The call requires the parameters be listed explicitly

Apply lets you invoke the function with arguments as an array.

The "constructor" property

Every object has a built-in property named constructor. It refers to the function which created it. Let us understand in detail:
1. function myFunction(a, b) {
2. return a * b; // Function returns the multiplication of a and b
3. }
4. var m = new myFunction();
5. console.log(m.constructor == myFunction); // true
6. console.log(m.__proto__.constructor == myFunction); // true, the other way to check is
Defining Your Own Function Properties

Many times we need a unique number say GUID or identifies which increments with each call made to function. In such a scenario, it is recommended to attach a property with a function. It is acting like a static property to keep track of the last value returned.
1. function myFunction(a, b) {
2. ++myFunction.p1;
3. return a * b; // Function returns the multiplication of a and b
4. }
5. myFunction.p1 = 1;
6. myFunction();
7. myFunction.p1; // will print 2
Length property

In a function, we pass arguments to process input, and sometimes we don’t pass the correct number of arguments. Therefore, it is good practice to check the required number of arguments needed for a particular function.
1. function myFunction(a, b) {
2. return a * b;
3. }
4. myFunction(2); // will give NaN because b is undefined
5. Its time to fix above
6. function by using property length
8. function myFunction(a, b) {
9. var argsRequired = arguments.length;
10. var argsActual = arguments.callee.length;
11. if(argsRequired != argsActual) {
12. throw new Error("Wrong # of args passed");
13. }
14. return a * b;
15. }

Summary

There are other useful properties also which you can look into detail. I hope you like this series. Please share your comments/feedback.

Read more articles on JavaScript

9 Comments

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Guest User10y ago
Thanks guys!!
Amit Dave10y ago
Keep up the Good work!
Amit Dave10y ago
Keep up the Good work!
Kuppurasu Nagaraj10y ago
Nice Sharing..
Bhuvanesh Mohankumar10y ago
Good one
Sonu Chaudhary10y ago
Thanks for sharing
Nitin10y ago
Thanks for sharing
Gowtham Rajamanickam10y ago
good one..
Thiruppathi R10y ago
Nice info

Introduction

Functions in-depth

Properties of function

Call v/s Apply

The "constructor" property

Defining Your Own Function Properties

Length property

Summary