JSFiddle - React, Tailwind, and code Playground

JavaScript

strng = "I have been working here till last six months"
text = ["since", "till", "until"]

var result;
for(var x = 0; x < text.length; x++){
    if(strng.indexOf(text[x]) > -1){
        result = text[x];
        break;
    }
}
alert(result);