It's just vanilla Javascript, not some "foreign way". Checking `"somestring".indexOf(something) != -1` is common idiom in JavaScript because function indexOf re

It's just vanilla Javascript, not some "foreign way". Checking `"somestring".indexOf(something) != -1` is common idiom in JavaScript because function indexOf returns -1 when there is no match. Just look for the definition of indexOf method on MDN: https://developer.mozilla.org/pl/docs/Web/JavaScript/Reference/Global_Objects/String/indexOf https://developer.mozilla.org/pl/docs/Web/JavaScript/Referen... Maybe it's weird but what else could indexOf return? It couldn't return 0, because strings in JS starts from 0 (not from 1), it couldn't return null, because JS is weak typed so in some circumstances null would be not different than 0. I'm glad that JS is not PHP (when some functions can return number or boolean or something else "just because") ;)