~ is the bitwise negation operator[MDN]. It converts its operand to a 32-bit integer and swaps all the 1s to 0s and all the 0s to 1s.
For example:
0000 0000 0000 0000 0000 0000 0000 0000 = 0
1111 1111 1111 1111 1111 1111 1111 1111 = ~0 = -1
Instead of doing text.indexOf(str) !== -1) you can use the tricky !~text.indexOf(str), because ~1 === 0 and !0 === true.
