# 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.

The following patterns are considered problems:

while (node) {                           /*error 'node' is not modified in this loop.*/
    doSomething(node);
}
node = other.

for (var j = 0; j < items.length; ++i) { /*error 'j' is not modified in this loop.*/
    doSomething(items[j]);
}

while (node !== root) {                  /*error 'node' is not modified in this loop.*/
                                         /*error 'root' is not modified in this loop.*/
    doSomething(node);
}

The following patterns are considered not problems:

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.

Version

This rule was introduced in ESLint 2.0.0-alpha-2.

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