Why Your Loop Runs Forever (and How to Actually Debug It)

We've all been there. You write a loop that looks perfectly reasonable, hit run, and watch your terminal freeze, your CPU spike to 100%, or your browser tab crash. Infinite loops are one of those bugs that feel embarrassing once you find the cause — but tracking them down can be genuinely tricky. Let me walk through the most common reasons loops go rogue, how to actually debug them when they do, and some patterns to prevent them from happening in the first place. The Obvious Ones (That Still Get Us) Before we get into the weird stuff, let's knock out the classics. Off-by-one errors and mutation mistakes account for probably 80% of accidental infinite loops I've seen in the wild. // Classic: forgetting to increment let i = 0 ; while ( i < 10 ) { console . log ( i ); // Oops — i never changes. This runs forever. } // Classic: mutating the wrong variable for ( let i = 0 ; i < items . length ; i ++ ) { items . push ( processItem ( items [ i ])); // array grows every iteration } The second