`indexOf` returns -1 if there's no match. Bitwise NOT on -1 will give you 0 -- for any other number, it'll return a truthy value. It's the same as: `return i

`indexOf` returns -1 if there's no match. Bitwise NOT on -1 will give you 0 -- for any other number, it'll return a truthy value. It's the same as: `return item.toLowerCase().indexOf(this.query.toLowerCase()) !== -1` If you're really dead set on doing things this way, it's safer to prefix with !! to coerce a real boolean: `return !!~item.toLowerCase().indexOf(this.query.toLowerCase())`