[рони]

Alexsandr,

"use strict"
const bigword = (str) => {
  let result = "";
  for (let i = 0; i < str.length; i++){

    if ( i === 0 || str.charAt(i) !== " " && str.charAt( i - 1 ) === " "  ) {
     result += str[i].toUpperCase();
    } else {
    result += str.charAt(i);
    }
  }
    return result;
}

alert(bigword(" привет тест"));