no-unmodified-loop-condition.md

Disallow unmodified conditions of loops (no-unmodified-loop-condition)

Variables in a loop condition often are modified in the loop. If not, it's possibly a mistake.

while (node) {
    doSomething(node);
}

while (node) {
    doSomething(node);
    node = node.parent;
}

Rule Details

This rule finds references which are inside of loop conditions, then checks the variables of those references are modified in the loop.

If a reference is inside of a binary expression or a ternary expression, this rule checks the result of the expression instead. If a reference is inside of a dynamic expression (e.g. CallExpression, YieldExpression, ...), this rule ignores it.

Examples of incorrect code for this rule:

/*eslint no-unmodified-loop-condition: "error"*/

while (node) {
    doSomething(node);
}
node = other;

for (var j = 0; j < items.length; ++i) {
    doSomething(items[j]);
}

while (node !== root) {
    doSomething(node);
}

Examples of correct code for this rule:

/*eslint no-unmodified-loop-condition: "error"*/

while (node) {
    doSomething(node);
    node = node.parent;
}

for (var j = 0; j < items.length; ++j) {
    doSomething(items[j]);
}

// OK, the result of this binary expression is changed in this loop.
while (node !== root) {
    doSomething(node);
    node = node.parent;
}

// OK, the result of this ternary expression is changed in this loop.
while (node ? A : B) {
    doSomething(node);
    node = node.parent;
}

// A property might be a getter which has side effect...
// Or "doSomething" can modify "obj.foo".
while (obj.foo) {
    doSomething(obj);
}

// A function call can return various values.
while (check(obj)) {
    doSomething(obj);
}

When Not To Use It

If you don't want to notified about references inside of loop conditions, then it's safe to disable this rule.