1//capitalize only the first letter of the string. 
2function capitalizeFirstLetter(string) {
3    return string.charAt(0).toUpperCase() + string.slice(1);
4}
5//capitalize all words of a string. 
6function capitalizeWords(string) {
7    return string.replace(/(?:^|\s)\S/g, function(a) { return a.toUpperCase(); });
8};

1const lower = 'this is an entirely lowercase string';
2const upper = lower.charAt(0).toUpperCase() + lower.substring(1);

1// for lowercase on first letter
2let s = "This is my string"
3let lowerCaseFirst = s.charAt(0).toLowerCase() + s.slice(1)

1function capitalizeFirstLetter(name) {
2    return name.replace(/^./, name[0].toUpperCase())
3}

1function titleCase(str) {
2   var splitStr = str.toLowerCase().split(' ');
3   for (var i = 0; i < splitStr.length; i++) {
4       // You do not need to check if i is larger than splitStr length, as your for does that for you
5       // Assign it back to the array
6       splitStr[i] = splitStr[i].charAt(0).toUpperCase() + splitStr[i].substring(1);     
7   }
8   // Directly return the joined string
9   return splitStr.join(' '); 
10}
11
12document.write(titleCase("I'm a little tea pot"));

1function capitalizeFirstLetter(str, inAllWordsOfString = false) {
2  if (!inAllWordsOfString) {
3    //convert given string to lowercase
4    let lowerStr = str.toLowerCase();
5    // Now convert first character to upper case
6    let firstCharacter = str.charAt(0).toUpperCase();
7    // Now combine firstCharacter and lowerStr and return
8    return firstCharacter + lowerStr.slice(1);
9  } else {
10    let str1 = str.split(" ");
11    let returnStr = "";
12
13    for (let i = 0; i < str1.length; i++) {
14      let lowerStr = str1[i].toLowerCase();
15      returnStr =
16        returnStr + str1[i].charAt(0).toUpperCase() + lowerStr.slice(1) + " ";
17    }
18    return returnStr.trim();
19  }
20}
21
22capitalizeFirstLetter('hello word');
23//output: Hello word
24
25capitalizeFirstLetter('hello word', true);
26//output : Hello Word