Repeat work with loops
Use for and while loops to repeat instructions without copying code.
- Use a for loop with a counter
- Use while for condition-controlled repetition
- Avoid infinite loops
A loop repeats a block of code. A for loop is handy when you know how a counter changes; a while loop repeats as long as a condition stays true.
for (let count = 1; count <= 3; count++) {
console.log(count);
}1 2 3
The for loop has a start (let count = 1), a condition (count <= 3) and an update (count++). Make sure each pass moves the condition toward false.
Key takeaways
Loops save you from repeating copied lines.
A for loop combines initialization, condition and update.
Check that a loop can eventually stop.
Lesson quiz
5 questions · pass with 4 correct · up to 50 XP
Passing this quiz completes the lesson and keeps your streak going. Questions you miss come back in review sessions later.
Practice: write JavaScript
Write the program, run it against the test cases, and use the feedback to build your JavaScript skills.
Sum to n
Read a positive whole number from input. Add every integer from 1 through that number, then print the sum.
- Sum through 5
- Sum through 10
JavaScript runs in a sandboxed browser frame with a 1.5 second time limit. Input is available as the string variable input.
Questions about this lesson
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