# for-direction

Disallow for loops which update their counter in the wrong direction.

A for loop with a counter may update its value in the wrong direction. that is to say, if i made a counter with a value of 0, if the for statement checked if counter < 10 and the update went counter--, that loop would be infinite. This is because counter will never be smaller than 10 because counter-- always yields a value smaller than 10. A for loop which does this is almost always a bug because it is either unreachable or infinite.

# Incorrect Code Examples

for (var i = 0; i < 10; i--) {
    /* infinite loop */
}

for (var i = 10; i >= 20; i++) {
    /* unreachable */
}

# Correct Code Examples

for (var i = 0; i < 10; i++) {
}

for (var i = 0; i < 10; i--) {}

for(let i = 0; i < 2; i--) {}

for(let i = 0; i <= 2; i += -1) {}

for(let i = 2; i >= 0; i -= -1) {}

for(let i = 0; i < 2; i -= 1) {}

for(let i = 2; i > 2; i++) {}

for(let i = 2; i > 2; i += 1) {}

for(let i = 5n; i < 2; i--) {}

for (var i = 0; i < 10; i++) {}

for(let i = 2; i > 2; i -= 1) {}

for(let i = 2; i >= 0; i -= 1) {}

for(let i = 2; i > 2; i += -1) {}

for(let i = 2; i >= 0; i += -1) {}

for(let i = 0; i < 3;) {}

for(let i = 5; i < 2; i |= 2) {}

for(let i = 5n; i < 2n; i &= 2) {}

Source (opens new window)