For Loop Explained in Depth
- The for loop is the most commonly used loop in JavaScript
- It is used when the number of iterations is known
Syntax of For Loop
for (initialization; condition; increment/decrement) {
// code to repeat
}
Breakdown:
- Initialization → Starting point (e.g.,
let i = 0) - Condition → Loop runs until this is true
- Increment/Decrement → Updates value after each iteration
Basic Example
for (let i = 0; i <= 10; i++) {
console.log(i);
}
Output:
0 to 10
Important:
<= 10→ includes 10< 10→ stops at 9
Understanding Off-by-One Concept
for (let i = 0; i <= 10; i++)
- Runs 11 times (0 to 10)
for (let i = 0; i < 10; i++)
- Runs 10 times (0 to 9)
Starting from Different Values
for (let i = 5; i <= 10; i++) {
console.log(i);
}
Output:
5 6 7 8 9 10
Increment by More Than 1
Increment by 2:
for (let i = 0; i <= 10; i += 2) {
console.log(i);
}
Output:
0 2 4 6 8 10
Increment by 3:
for (let i = 1; i <= 10; i += 3) {
console.log(i);
}
Reverse Loop (Decrement)
for (let i = 10; i >= 0; i--) {
console.log(i);
}
Output:
10 9 8 ... 0
Nested Loops
- A loop inside another loop
Example:
for (let i = 0; i <= 3; i++) {
for (let j = 0; j <= 2; j++) {
console.log("j:", j);
}
console.log("-----");
}
Key Point:
- Inner loop runs completely for each iteration of outer loop
Important Rule for Nested Loops
- Use different variables (
i,j) - Avoid using same variable → can cause bugs or infinite loops
Printing Tables Using For Loop
Example: Table of 10
for (let i = 1; i <= 10; i++) {
console.log(10 * i);
}
Example: Table of 34
for (let i = 1; i <= 10; i++) {
console.log(34 * i);
}