JavaScript Loops

Loops are the main component of every programming language. Iteration or loop is a structure, series, or process, the end of which is connected to the beginning. But in programming, it allows repeating block code, until the given condition is true. In Javascript we have three basics types loops are available –

• for
• while
• do while

for loop

// for loop 
for (var i = 0; i < 5; i++) {
    console.info(i); // 0, 1, 2, 3, 4
}

while loop

// while loop
var i = 0;
while (i < 5) {
    console.log(i); // 0, 1, 2, 3, 4
    i++;
}

do while loop

// do while loop
var i = 0;
do {
    console.log(i); // 0, 1, 2, 3, 4
    i++;
} while( i< 5);

continue

continue to exit the current iteration in a loop.

for (var i = 0; i < 5; i++) {
    if ( i % 2 == 0) continue; //skip this iteration
    console.log(i); // 1, 3
}

break

break exits the loop completely.

for (var i = 0; i < 5; i++) {
    if ( i % 2 != 0) break; // exits loop 
    console.log(i); //0
}

for in loop

for in for object don’t use it for an array

var obj = { 
    name: "Jhon",
    age: 23 
};

for (var key in obj) {
    console.log(obj[key]); //Jhon, 23
}

forEach loop

// forEach loop

var obj = ["Jhon",23 ];

obj.forEach(function (key, val) {
    console.log(val); // 0, 1
});

for…of

for-of is a new loop in ES6 that replaces both for-in and forEach() and supports the new iteration protocol.

// forEach loop
let arr = [1, 2, 3];

for (let val of arr) {
	console.info(val); // 1, 2, 3
}