Mastering the for Loop in JavaScript
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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.
An iteration is one full execution of the loop body.
123for (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:
123for (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:
12345678let 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:
123for (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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