Loops in ECMAScript 6

A Loop statement can be defined as a group of instructions that are always repeated. In the computer programming language, the loops help us to execute a collection of instructions that repeats again and again till the condition is true. In the loop statement, the repetition of a statement is defined as an iteration.

Classification of Loops

Loops in ECMAScript 6

Now, we are going to discuss each category of the loop in detail.

Definite Loops

This type of loop has a definite/ fixed/ constant number of iterations. There are the following three types of definite loops used in ECMAScript 6.

Loop             Description
             For (; 😉 loop The for loop is used to execute the block code for a particular number of times within a termination condition.
             For…in loop The for…in loop is used to execute the block code by using the properties of an object.
             For…of loop The for…of loop is used to execute the iterables (string, array) instead of object literals.

Now, we are going to discuss each loop with syntax and example.

The For (; ; ) loop

The for loop helps us to execute the block code for a particular number of times. It means if we have a constant number of iterations, then we will use a for loop.

Syntax

The for (; 😉 loop contains the following elements-

Initialization: It is a process to initialize the variables and also used for existing initialized variables. Initialization is optional to use.

Condition: It always executes to check the loop condition. It always returns True/False (Boolean value). It executes until the loop condition is false. In ECMAScript, it is optional to use.

Increment/ Decrement: It is used to increase or decrease the value of a variable by 1(+1 /-1). It is also optional to use.

Flowchart of for (; 😉 loop

Loops in ECMAScript 6

There are some examples given below, which represents the various kind of for loop.

Example 1

Here is an example of a simple for loop.

Output

Loops in ECMAScript 6

Here, we will try to illustrate the code of for loop with multiple expressions.

Example 2

The below-given code helps us to understand the concept of for loop with multiple expressions.

Output

After the execution of the above code, we will get the following output

Loops in ECMAScript 6

In the program code, we can easily merge the multiple expressions and assignments within a single loop by using comma (,).

Example 3

Here is an example of infinite for loop.

Output

Loops in ECMAScript 6

If we want to terminate this infinite loop then we will use Ctrl + C.

The For…in Loop

The for…in loop is similar to for loop, but it iterates the block code by using the properties of an object (The object keys). We can use a for…in loop when we are dealing with objects where the index order is not necessary.

In each iteration of the for…in loop, one property is allotted to the variable name. The loop executes the condition until the object have at least one property left. The for…in loop comes under the category of definite loops.

Syntax

Example

Output

After execution of the code, we will get the following output.

Loops in ECMAScript 6

If we pass a function as the properties of the object then we will get the whole function as the output. We will try to implement it with the following example.

Output

After execution of the code, we will get the following output.

Loops in ECMAScript 6

In the code mentioned above, the function price () is returned as the output.

The For…of loop

The for…of loop is used to execute the iterables (array, string) instead of object literals.

In each iteration of for…of loop, one property is allotted to the variable name. The loop executes the condition until the object has at least one iteration left. The for…of loop comes under the category of definite loops.

Syntax

Example

Output

After the execution of the above example, we will get the following output.

Loops in ECMAScript 6

Indefinite Loop

The Indefinite loop has an unknown or transitional number of iterations inside the loop. In the Indefinite loop, we have an infinite number of iterations. There are following two types of indefinite loops listed below:

                      Loop                       Description
                While loop This loop is used to execute the condition until a particular condition is true. The condition classifies before the code statement is executed.
                 Do…while loop It is similar to a while loop, but the difference is; the do…while loop executes the code statement at one time without checking the condition.

Now, we are going to discuss each loop with syntax and example.

While Loop

The while loop is considered as a control statement. It is used to execute the program code in a repeated way based on the given Boolean condition. This loop is also known as “the pre-test loop.” In the while loop, we can check the condition before the execution of the block code.

The while loop contains; condition/ expression and block of code. The while loop comes under the category of Indefinite loop.

Syntax

Flowchart of While loop

Loops in ECMAScript 6

Example

Here, we discuss the example of while loop.

Output

After the successful execution of the example, we will get the following output.

Loops in ECMAScript 6

Note-          

  • When the condition is true, then the loop will be executed.
  • The condition/ expression is necessary to execute the loop.
  • If the condition is true, then the loop always executes, but if the condition is false, then the loop will terminate.

Do…while Loop

The Do…while loop is a control statement. It is used to execute the code block at least once before condition check; if the condition is true, then the loop executes continuously; otherwise, the loop will be terminated. The Do…while loop is also known as “the post-test loop”. This loop comes under the category of Indefinite loop.

Syntax

Flowchart of Do…while loop

Loops in ECMAScript 6

Example

Here, we discuss an example of Do…while loop.

Output

After the execution of the above code, we will get the following output.

Loops in ECMAScript 6

Difference between While and Do…while loop

                While Loop                    Do…while Loop
It checks the conditions before the execution. It checks condition after the execution.
It executes the code block if and only if the condition is true. It executes the code block at least once; even the condition is false later.
It is defined as an entry-controlled loop. It is defined as an exit-controlled loop.
We can use it when the condition is important. We can use it when the process is more important.
The semicolon (;) is not compulsory after the end of the while loop.                  The semicolon (;) is compulsory after the end of the do…while loop.                  
Syntax              while (condition) {               // statement }       Syntax               do {                         // statement } while (condition)         

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