Define and Use the Functions

Function

We can divide a program into procedural components or modules called functions in JavaScript. We are already familiar with functions like console.log(), prompt(), and length(). Functions can be copied and reused in a programming technique called a modular or procedural approach, also known as the divide and conquer approach. We should always try to design functions that can be reused in other programs too.

Broadly, there are two types of functions, which we’ll explore in the following sections.

Structure of a function

The following slides illustrate various parts of a function definition:

A function name can only contain letters (A—Z and a—z) and the underscore symbol (_). It may also contain digits (0–9), but the function name can’t start with those. For example, Key_2 is a valid function name, but 2_key is not. Function names are case-sensitive, meaning that name, Name, and NAME are three different functions.

There are two main parts of a function definition:

• Header: The first line, with a pair of brackets.

• Body: The block of statements with the function boundaries.

The function header contains the keywordThe keywords are predefined by the language. function, the function name sayHello, the parameters in (), and a pair of curly brackets to indicate the start and the end of the body. All the statements in the function body are written as a block of code enclosed in { and }. We can not write the body of the function without braces.

Let’s write code for the above example.

In the last line, we’re telling the program to run the function sayHello(). This line is known as a function call or calling the function.

Example of function calls

Let’s look at the following code:

In the program:

• We define two simple functions—first and second.

• We demonstrate the sequence of execution with the help of console.log statements.

The return statement

The following slides illustrate another function that returns a value. The example shows (1) how to use the return statement in the function body and (2) how to write the parameters (a,b) in the function header.

Let’s write out the code for the above example.

In the above code:

• The last line calls the console.log() function. It invokes the getSum() function with the values 5 and 6 as arguments for the parameters a and b, respectively.

• The variable, mysum, holds the sum of a and b, which is 11.

• The statement, return mysum;, returns 11 to the console.log() statement as a result of the function call.

Note: Any statement written in the function body after the return statement is unreachable.

Practice creating and calling functions

The following are a few example programs to practice creating and calling functions. By clicking the “Show Solution” button, you’ll find a program that solves the respective problem. You can copy and paste the given solution into the code widget to make sure that the output of your solution matches the given solution. There may be several ways of writing correct solutions in programming.

Function to create a multiplication table

Write a function showTableOf4() that displays 20 terms of the table of 4. Call your function to display the results.

Sample output

4 x 1 = 4
4 x 2 = 8
4 x 3 = 12
4 x 4 = 16
4 x 5 = 20
4 x 6 = 24
4 x 7 = 28
4 x 8 = 32
4 x 9 = 36
4 x 10 = 40
4 x 11 = 44
4 x 12 = 48
4 x 13 = 52
4 x 14 = 56
4 x 15 = 60
4 x 16 = 64
4 x 17 = 68
4 x 18 = 72
4 x 19 = 76
4 x 20 = 80

Function to find distinct values

Write a function showDistinct that takes a list as a parameter and prints the distinct elements in the array. It’s assumed that the array is already sorted in ascending order. Call your function to display the results.

Sample input 1

[2, 5, 5, 8, 8, 8, 9, 30, 45]

Sample output 1

Original array: 2, 5, 5, 8, 8, 8, 9, 30, 45
Distinct array: 2, 5, 8, 9, 30, 45

Sample input 2

[2, 5, 5, 8, 8, 8]

Sample output 1

Original array: 2,5,5,8,8,8
Distinct array: 2,5,8

Function to search a string in an array

Write a function that checks if a string is present in the array. If it’s present, display its index in the array. Call your function to display the results.

Sample input 1

• First parameter: array

  ['2','55','888','9','30','45']
  

• First parameter: string

  '888'
  

Sample output 1

 888 is found at index 2

Sample input 2

• First parameter: array

  ['2','55','888','9','30','45']
  

• First parameter: string

  '50'
  

Sample output 2

***  50 is NOT FOUND in the array ***

Function to display the Fibonacci sequence

A Fibonacci sequence is a sequence in which each number is the sum of the two preceding ones. Write a function, fibo, that receives the parameter n to specify the number of terms of the Fibonacci sequence. That function will return a list containing the sequence. Call your function to display the results.

Sample input

10

Sample output

First 10 terms of Fibonacci sequence are: 0,1,1,2,3,5,8,13,21,34
*** End of generating Fibonacci Numbers ***