String Find in TypeScript

In TypeScript, you can find the index of a substring using indexOf():

s.indexOf(sub)         // returns index of first occurrence, or -1 if not found
s.lastIndexOf(sub)     // returns index of last occurrence
s.indexOf(sub, start)  // search starting from index `start`

Here are some examples:

let sentence = "Hello World";
let idx = sentence.indexOf("World");
console.log(idx);  // 6

console.log(sentence.indexOf("xyz"));  // -1  (not found)

The index returned is the position of the first character of the found substring.