JavaScript Loops

Loops are used to execute a block of code continuously until a specific condition is met. They are useful for automating repetitive tasks, such as iterating over arrays or processing data.

Types of Loops

JavaScript supports several types of loops:

• for loop
• while loop
• do...while loop
• for...in loop
• for...of loop

For Loop

The for loop is the most commonly used loop. It repeats a block of code a specified number of times.

Syntax:

for (initialization; condition; increment/decrement) {
  // code to be executed
}

Example:

for (let i = 0; i < 5; i++) {
  console.log("Iteration number: " + i);
}

While Loop

The while loop executes a block of code as long as a specified condition is true.

Syntax:

while (condition) {
  // code to be executed
}

Example:

let i = 0;
while (i < 5) {
  console.log("Count: " + i);
  i++;
}

Do…While Loop

The do...while loop is similar to the while loop, but it guarantees that the code block is executed at least once before checking the condition.

Syntax:

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

Example:

let i = 0;
do {
  console.log("Count: " + i);
  i++;
} while (i < 5);

For…In Loop

The for...in loop iterates over the properties of an object.

Syntax:

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

Example:

const person = { fname: "John", lname: "Doe", age: 25 };
for (let x in person) {
  console.log(person[x]);
}

For…Of Loop

The for...of loop iterates over the values of an iterable object (like an array, string, map, or set).

Syntax:

for (variable of iterable) {
  // code to be executed
}

Example:

const cars = ["BMW", "Volvo", "Mini"];
for (let x of cars) {
  console.log(x);
}

Break and Continue

Break

The break statement “jumps out” of a loop.

for (let i = 0; i < 10; i++) {
  if (i === 3) {
    break;
  }
  console.log("The number is " + i);
}

Continue

The continue statement breaks one iteration (in the loop), if a specified condition occurs, and continues with the next iteration in the loop.

for (let i = 0; i < 10; i++) {
  if (i === 3) {
    continue;
  }
  console.log("The number is " + i);
}