JavaScript While Loops
While Loops
While loops execute a block of code as long as a specified condition is true.
JavaScript have two types of while loops:
- The while loop
- The do while loop
The While Loop
The while loop loops through a block of code as long as a specified condition is true.
Syntax
while (condition) {
// code block to be executed
}
In the following example, the code in the loop will run, over and over again, as long as a variable (i) is less than 10:
If you forget to increase the variable used in the condition, the loop will never end.
This will crash your browser.
The Do While Loop
The do while loop is a variant of the while loop. This loop will
execute the code block once, before checking if the condition is true, then it will
repeat the loop as long as the condition is true.
Syntax
do {
// code block to be executed
}
while (condition);
The do while runs at least once, even if the condition is false from the start.
This is because the code block is executed before the condition is tested:
Do not forget to increase the variable used in the condition, otherwise the loop will never end!
Comparing For and While
A while loop is much the same as a for loop, with statement 1 and statement 3 omitted.
Example
Uses a for loop to collect the car names from the cars array:
const cars = ["BMW", "Volvo", "Saab", "Ford"];
let i = 0;
let text = "";
for (;cars[i];) {
text += cars[i];
i++;
}
Try it Yourself »
Example
Use a while loop to collect the car names from the cars array:
const cars = ["BMW", "Volvo", "Saab", "Ford"];
let i = 0;
let text = "";
while (cars[i]) {
text += cars[i];
i++;
}
Try it Yourself »
