JSFiddle - React, Tailwind, and code Playground

JavaScript

var string = 'Samwise gamgee meRRy';
var substr = ['sam', 'samwise', 'merry', 'pippin'];

var matches = substr.map(function(v) {
  var re = new RegExp("\\b" + v, "i"); var m = re.exec(string); 
  return (m !== null ? m[0] : false);
}).filter(Boolean);

console.log(matches);