function titleCaseWord(word: string) {
  if (!word) return word;
  return word[0].toUpperCase() + word.substr(1).toLowerCase();
}

You can also use in template TitleCasePipe

Some component template:

{{value |titlecase}}

 let str:string = 'hello';
 str = str[0].toUpperCase() + str.slice(1);

var str = 'santosh';
str = str ? str.charAt(0).toUpperCase() + str.substr(1).toLowerCase() : '';