js-loop.md

JavaScript Loop

Summary

for Loop

Use for to execute a block of code for a specified number of times.

for (let i = 0; i < <number>; i++) {
    // block of code to be executed
}

<number> represents the number of times the block of code is executed. It must be a number.

Example:

for (let i = 0; i < 10; i++) {
    console.log(i);
}

while Loop

Use while to execute a block of code while a specified condition is true.

while (<condition>) {
    // block of code to be executed while the condition is true
}

<condition> is a condition that must be true or false.

Example:

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

do...while Loop

Use do...while to execute a block of code at least once, then repeat the block of code while a specified condition is true.

do {
    // block of code to be executed at least once then repeat while the condition is true
} while (<condition>);

<condition> is a condition that must be true or false.

Note

A do...while loop is similar to a while loop, except that it executes the block of code at least once before checking the condition.

Example:

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

for...in Loop

Use for...in to loop through the properties of an object.

for (let key in object) {
    // block of code to be executed
}

<key> is each key of the object you want to loop through. <object> is an object.

Example:

let object = {
    a: 1,
    b: 2,
    c: 3
}

for (let key in object) {
    console.log(key + ":", object[key]); // Output: a: 1, b: 2, c: 3
}

for...of Loop

Use for...of to loop through the values of an array.

for (let value of array) {
    // block of code to be executed
}

<value> is each value of the array you want to loop through. <array> is an array.

Example:

let array = [1, 2, 3];

for (let value of array) {
    console.log(value); // Output: 1, 2, 3
}