for-direction.md

Pattern: Incorrect for loop counter direction

Issue: -

Description

A for loop with a stop condition that can never be reached, such as one with a counter that moves in the wrong direction, will run infinitely. While there are occasions when an infinite loop is intended, the convention is to construct such loops as while loops. More typically, an infinite for loop is a bug.

Examples

Example of incorrect code:

for (var i = 0; i < 10; i--) {}
for (var i = 10; i >= 0; i++) {}
for (var i = 0; i > 10; i++) {}
for (var i = 0; 10 > i; i--) {}
const n = -2;
for (let i = 0; i < 10; i += n) {}

Example of correct code:

for (var i = 0; i < 10; i++) {}
for (var i = 0; 10 > i; i++) {
  // with counter "i" on the right
}
for (let i = 10; i >= 0; i += this.step) {
  // direction unknown
}
for (let i = MIN; i <= MAX; i -= 0) {
  // not increasing or decreasing
}