Programming Tutorials

(追記) (追記ここまで)

while and do-while in JavaScript

By: Stella in Javascript Tutorials on 2023年04月25日 [フレーム]

In JavaScript, while and do-while are two types of loops that can be used to repeat a block of code multiple times.

The while loop executes a block of code while a specified condition is true. The syntax for a while loop is:

while (condition) {
 // code to be executed while the condition is true
}

Here, condition is a Boolean expression that is evaluated at the beginning of each iteration. If the condition is true, the code inside the loop is executed. If the condition is false, the loop is terminated and the program continues with the next statement after the loop.

For example, the following code uses a while loop to print the numbers from 1 to 5:

let i = 1;
while (i <= 5) {
 console.log(i);
 i++;
}

The do-while loop is similar to the while loop, but with one key difference: the code inside the loop is executed at least once, even if the condition is false. The syntax for a do-while loop is:

do {
 // code to be executed at least once
} while (condition);

Here, the code inside the do block is executed first, and then the condition is evaluated. If the condition is true, the loop continues and the code inside the do block is executed again. If the condition is false, the loop is terminated and the program continues with the next statement after the loop.

For example, the following code uses a do-while loop to prompt the user for a number between 1 and 5:

let num;
do {
 num = prompt("Enter a number between 1 and 5:");
} while (num < 1 || num > 5);
console.log("You entered: " + num);

In this example, the do block prompts the user for a number, and then the while condition checks whether the number is between 1 and 5. If the number is not between 1 and 5, the loop continues and the user is prompted again. If the number is between 1 and 5, the loop is terminated and the program continues with the console.log statement.

Previous
<< == vs === in JavaScript

Next
for, for..of, and for..in loops in JavaScript>>

(追記) (追記ここまで)