The for loop is a common way to repeat code. It uses three parts inside the parentheses:

for (Initialization; Condition; Increment/Decrement) {
  // code block
}

What each part means:

Initialization: creates the loop counter (runs once);
Condition: checked before every iteration;
Increment/Decrement: updates the counter after each loop.

Note

An iteration is one full execution of the loop body.


              123
            
for (let i = 1; i < 5; i++) {
  console.log("Loop iteration:", i);
};

let i = 1: initialization;
i < 5: condition;
i++: increment;
console.log(...): loop body.

This repeats until the condition becomes false.

You can also use decrement in the for loop, as shown here:


              123
            
for (let i = 15; i > 10; i--) {
  console.log("i =", i);
}

The for loop counter is unique to its scope, so you don't need to worry about the counter name conflicting with other variables:


              12345678
            
let i = 2077;
console.log("(global) i =", i);

for (let i = 0; i < 4; i++) {
  console.log("(for) i =", i);
}

console.log("(global) i =", i);

Different expressions for Increment/Decrement operations can be used as well:


              123
            
for (let i = 0; i < 40; i += 7) {
  console.log("i =", i);
};

Comparing the for and while loops

When comparing for and while loops, the for loop is often simpler and more concise. Here's an example of equivalent loops:


              1234567891011
            
// `while`
let a = 1;
while (a <= 3) {
  console.log("While:", a);
  a++;
}

// `for`
for (let i = 1; i <= 3; i++) {
  console.log("For:", i);
}

The for loop is usually shorter and keeps the counter inside its own scope.

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Section 5. Chapter 3

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The for loop is a common way to repeat code. It uses three parts inside the parentheses:

for (Initialization; Condition; Increment/Decrement) {
  // code block
}

What each part means:

Initialization: creates the loop counter (runs once);
Condition: checked before every iteration;
Increment/Decrement: updates the counter after each loop.

Note

An iteration is one full execution of the loop body.


              123
            
for (let i = 1; i < 5; i++) {
  console.log("Loop iteration:", i);
};

let i = 1: initialization;
i < 5: condition;
i++: increment;
console.log(...): loop body.

This repeats until the condition becomes false.

You can also use decrement in the for loop, as shown here:


              123
            
for (let i = 15; i > 10; i--) {
  console.log("i =", i);
}

The for loop counter is unique to its scope, so you don't need to worry about the counter name conflicting with other variables:


              12345678
            
let i = 2077;
console.log("(global) i =", i);

for (let i = 0; i < 4; i++) {
  console.log("(for) i =", i);
}

console.log("(global) i =", i);

Different expressions for Increment/Decrement operations can be used as well:


              123
            
for (let i = 0; i < 40; i += 7) {
  console.log("i =", i);
};

Comparing the for and while loops

When comparing for and while loops, the for loop is often simpler and more concise. Here's an example of equivalent loops:


              1234567891011
            
// `while`
let a = 1;
while (a <= 3) {
  console.log("While:", a);
  a++;
}

// `for`
for (let i = 1; i <= 3; i++) {
  console.log("For:", i);
}

The for loop is usually shorter and keeps the counter inside its own scope.

Everything was clear?

Thanks for your feedback!

Section 5. Chapter 3

Mastering the for Loop in JavaScript

Comparing the for and while loops

Mastering the for Loop in JavaScript

Comparing the for and while loops