While Loop in JavaScript

Introduction on While Loop in Javascript

Today we are concentrating on a while loop. Looping is nothing but the doing task repeatedly over and over. Suppose we have to print some no. for example 1 to 10. In this scenario, if we think we have to write a print statement 10 times for each no. code will be more and it is time-consuming. And most important it is repetitive. While coding in any language we have to consider DRY policy. That means Don’t Repeat Yourself (DRY). In this topic, we are going to learn about While Loop in JavaScript.

So, here loops come into the picture. In that while loop. If you think about the simple English language then you will understand better. Simple while meaning is at the same time or to a period. The same applies here in a programming language also. While the condition is true the particular code will execute.

While loop checks the condition, whether it is true or false. If the condition is true it simply runs the code till the breakpoint. If the condition is false it does not go ahead.

Syntax:

While(condition){
// code to execute
}

In a while loop, we are checking the condition at the time of starting the loop, so we can decide to execute it or not. In a while loop, we have some block of statements. Which will get in execution-only the condition specified in that loop is true.

We often use true as true and false. if you know the binary concept in programming then it will be easier to understand.

True and false are the two values used to evaluate the expression. While checking the condition and executing program this will be helpful.

Look at the following syntax for true and false:

While(true){
// code will execute
}
While(false){
// code will not execute
}

Example

while(true){
console.log("Hello");
break;
}

Output:

In the case of zero, we will directly come out of the loop.

Example

var i = 0;
while (i < 10) {
console.log(i);
i++;
}

Output:

How Does While Loop Work in Javascript?

The while loop is very simple to understand. We know that loops are used in programming to automate the different repetitive tasks. But we need to take some precautions at a point where we are not increasing it. To get a more clear idea about this so let’s check the following example.

Example

The following code is with increment operator ++.

var i=1;
while (i<=5){
console.log("Hello");
i++;
}

Output:

Now, Let’s see some code without the increment operator. Please try out the following code.

In JavaScript, you have to declare the variable and initialize it. Skipping this process may cause run time errors in a compiler.

 var i=1;
while (i<=5){
console.log("Hello");
i++;
}

Output:

Please run above code and you will see that code is running infinitely.

There is no stop for printing name Hello. To make sure that we should get particular no of words as an output we must be using increment or decrement operator along with while loop.

Flow Diagram

In general, the loop is divided into 3 parts.

1. Initialization: assigning value to the variable
2. Condition: condition to check it is true or false
3. Increment or decrement: these operators are useful in incrementing the loop automatically or decrementing the loop.

We will closely look into all these states of the loop in the upcoming example.

The important part of any program is its logic. Look carefully at below flowchart at the start of the program we need to initialize the variable.

Initializing is nothing but assigning value to that variable to be used. Upon initialization, we are good to apply while loop. in a while loop, we are checking the condition. for example, i <=5. here loop will start if the condition is true. If the condition is false then we will get directly out of the loop. In general, when we are talking about getting out of the loop we need increment (++) and decrement (–) operators.

Examples

Let’s think of an example with the decrement operator. Till now we have seen the while loop with increment operator (++). Now, we will observe decrement (–) operator. The decrement operator as name suggest reduces the value of a variable as per requirement given. Loop will stop when the condition gets false.

Example:

var i=5;
while (i>=1){
console.log("Hello World");
i--;
}

Output:

If you run the above program you will find the same output as you have seen it with the increment operator.

Example:

fruits = 1;
while (fruits <= 5) {
console.log(fruits + " has to be there");
fruits++;
}
console.log("there are total " + (fruits - 1) + " rounds to market.");

Output:

Example: While loop with the array

var fruits = ["Apple","Banana","Kiwi","Pinaple"];
total = 0;
while (total < fruits.length) {
console.log("There is " + fruits[total]+ " in the basket");
total++;
}

Output:

Example

var balance = 0;
var greet = "";
while (balance <= 10) {
greet = greet + "\n I have added $" + balance+ " in my account";
balance ++;
}
console.log(greet);

Output:

In all the above examples we have seen how can we work with a while loop. Looping is possible when the condition gets true. Change the conditions. Try with true and false statements. Observe the output.

While the loop always checks the condition. If the condition is true then it gets executed.

It saves us from doing repetitive work again and again. So try it several times and get your hands dirty.

Conclusion

Loops play an important role in programming. As they help to reduce repetitive tasks and do it by making it automatically. If we have correct logic then the loop saves lots of time of a programmer.

Recommended Articles

This is a guide to While Loop in JavaScript. here we discuss How Does While Loop Work in Javascript with the Examples, Flow Diagram and Outputs. You may also have a look at the following articles to learn more –

1. While Loop in Java
2. Loops in R
3. Arrays in JavaScript
4. Loops in C