The for loop

Learn the for loop structure: counter, condition and increment steps.

The for loop runs a block a fixed number of times. Its header has three parts: init, condition and increment.

for (let i = 1; i <= 3; i++) {
  console.log(i);
}

Here i is the counter. Each step tests the condition; if true, it runs the block and increments. When false, the loop ends.

Sum and count patterns

The for loop is commonly used for two tasks: accumulating a sum, or walking through a sequence.

Sum example:

let total = 0;
for (let i = 1; i <= 5; i++) {
  total = total + i;
}
console.log(total); // 15

Here total is the accumulator. Each step adds i to it. When the loop ends, total is 1+2+3+4+5 = 15.

Use a for loop to print the numbers 1 to 5 with console.log.

Show example solution

for (let i = 1; i <= 5; i++) {
  console.log(i);
}

Use a for loop to compute the sum of numbers 1 to 10. Accumulate it in a total variable and finally print it with console.log(total).

Show example solution

let total = 0;
for (let i = 1; i <= 10; i++) {
  total += i;
}
console.log(total);

Complete the loop that counts down from 5 to 1

for (let i = 5; i >= ____; i--) { console.log(i); }

Show answer

for (let i = 5; i >= 1; i--) { console.log(i); }