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Loops can execute a block of codeas long as a specified condition is true
The while
loop loops through a block of code as long as a specified condition is true.
Syntax
Example
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:
while (i < 10) {
text += "The number is " + i;
i++;
}
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 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
Example
The example below uses a do while
loop. The loop will always be
executed at least once, even if the condition is false, because the code block
is executed before the condition is tested:
do {
text += "The number is " + i;
i++;
}
while (i < 10);
Do not forget to increase the variable used in the condition, otherwise the loop will never end!
If you have read the previous chapter, about the for loop, you will discover that a while loop is much the same as a for loop, with statement 1 and statement 3 omitted.
The loop in this 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++;
}
The loop in this example uses 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++;
}
Create a loop that runs as long as i
is less than 10.
let i = 0; (i 10) { console.log(i); i++ }