JavaScript, finds first occurrence of a string within another, case insensitive. Inspiration from the similar PHP function.

stristr.js

function stristr (haystack, needle, bool) {
    var pos = 0;
   
    haystack += '';
    pos = haystack.toLowerCase().indexOf((needle + '').toLowerCase());
    if (pos == -1) {
        return false;
    } else {
        if (bool) {
            return haystack.substr(0, pos);
        } else {
            return haystack.slice(pos);
        }
    }
}

console.log( stristr('Aenean et iaculis odio, at iaculis libero. Donec ultricies dui et congue lobortis. potenti.', 'dui') );
// will return `dui et congue lobortis. potenti.`
console.log( stristr('Aenean et iaculis odio, at iaculis libero. Donec ultricies dui et congue lobortis. potenti.', 'dui', true) );
// will return `Aenean et iaculis odio, at iaculis libero. Donec ultricies `