javascript - 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 adding the broken string but how does the (1) work?

function toUpper(str) {
return str
    .toLowerCase()
    .split(' ')
    .map(function(word) {
        return word[0].toUpperCase() + word.substr(1);
    })
    .join(' ');
 }
 console.log(toUpper("hello friend"))

Answer 1

The return value contain 2 parts:

return word[0].toUpperCase() + word.substr(1);

1) word[0].toUpperCase(): It's the first capital letter

2) word.substr(1) the whole remain word except the first letter which has been capitalized. This is document for how substr works.

Refer below result if you want to debug:

function toUpper(str) {
return str
    .toLowerCase()
    .split(' ')
    .map(function(word) {
        console.log("First capital letter: "+word[0]);
        console.log("remain letters: "+ word.substr(1));
        return word[0].toUpperCase() + word.substr(1);
    })
    .join(' ');
 }
 console.log(toUpper("hello friend"))