Capitalize first letter of each word in JS

Question

I\'m learning how to capitalize the first letter of each word in a string and for this solution I understand everything except the word.substr(1) portion. I see that it\'s a

Answer 1

function titlecase(str){
   let titlecasesentence = str.split(' ');
   titlecasesentence = titlecasesentence.map((word)=>{
     const firstletter = word.charAt(0).toUpperCase();
     word = firstletter.concat(word.slice(1,word.length));

     return word;
});
  titlecasesentence = titlecasesentence.join(' ');
  return titlecasesentence;
}
titlecase('this is how to capitalize the first letter of a word');