JavaScript Loops & Iteration

You are reading Part 5 of the 39-part series: JavaScript Skill Progression: The Path from Beginner to Extreme. [Level 1]

Introduction

Loops are fundamental in programming, allowing developers to execute a block of code multiple times efficiently. JavaScript provides several looping mechanisms, including for, while, and do-while loops. Understanding these loops is crucial for writing efficient and maintainable code.

Loops are essential for iterating over data, automating repetitive tasks, and implementing efficient algorithms. Mastering for, while, and do-while loops will significantly enhance your JavaScript programming skills, making your code more efficient and readable.

The for Loop

The for loop is commonly used when the number of iterations is known beforehand. It consists of three parts:

1. Initialization – Declares and initializes a loop variable.

2. Condition – Specifies the condition that must remain true for the loop to continue.

3. Increment/Decrement – Updates the loop variable after each iteration.

Syntax:

for (initialization; condition; increment/decrement) {
    // Code to execute in each iteration
}

Example:

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

The while Loop

The while loop executes a block of code as long as a specified condition evaluates to true. It is useful when the number of iterations is unknown and depends on dynamic conditions.

Syntax:

while (condition) {
    // Code to execute as long as the condition is true
}

Example:

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

The do-while Loop

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

Syntax:

do {
    // Code to execute at least once
} while (condition);

Example:

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

Loop Control Statements

JavaScript provides additional control mechanisms to modify loop execution:

• break Statement – Terminates the loop immediately.

  for (let i = 0; i < 10; i++) {
      if (i === 5) break;
      console.log(i);
  }
  

• continue Statement – Skips the current iteration and moves to the next.

  for (let i = 0; i < 10; i++) {
      if (i % 2 === 0) continue;
      console.log(i);
  }
  

Choosing the Right Loop

• Use for loops when the number of iterations is predetermined.

• Use while loops when the iterations depend on dynamic conditions.

• Use do-while loops when you need to ensure the loop runs at least once.

You are reading Part 5 of the 39-part series: JavaScript Skill Progression: The Path from Beginner to Extreme. [Level 1]