Detect occurrences of the comma operator in expressions. The comma operator can make code harder to read and debug, as it executes multiple expressions but only returns the value of the last one.
The comma operator evaluates each of its operands (from left to right) and returns the value of the last operand. This behavior is often confusing and rarely intended, reducing code readability and increasing the potential for bugs. Clearer alternatives using separate statements are preferred.
Side-by-side examples engineers can pattern-match during review.
let x = 0;
const y = (x++, x + 1); // Bad: y becomes 2, x becomes 1. Confusing.let x = 0;
x++;
const y = x + 1; // Good: Clear separation of steps.i = a += 2, a + b;a += 2;
i = a + b;From the same buckets as this rule.
Check if loops use equality operators (== or !=) in termination conditions. These can lead to infinite loops if the condition is never met exactly. Instead, use relational operators like < or > for safer loop termination.