const index = str.search(/\d/);
.const index = str.match(/^(\D*\d)?/)[0].length - 1;
// или
const index = [...str].findIndex(n => !Number.isNaN(Number(n)));
// или
let index = -1;
for (let i = 0; i < str.length; i++) {
if ('0123456789'.includes(str.charAt(i))) {
index = i;
break;
}
}
// или
const index = (function get(i, n = str[i]) {
return (
!n ? -1 :
+n === +n ? i :
get(-~i)
);
})(0);