Five ways to search strings in Javascript

1) Introduced with EcmaScript 6, for most scenarios .includes is superb, always returning a boolean:
const string = `Let's search this string for a substring`
const substring = `his`
string.includes(substring) 
// => true
2) .match is a bit more verstile, returning an informative array on success or null when nothing found:
const string = `Let's search this string for a substring`
const expr = /his/; // you can go wild here
string.match(expr);
// => ["his", index: 14, input: "Let's search this string for a substring", groups: undefined]
3) Oldies, but goodies .indexOf always gets the job done:
const string = `Let's search this string for a substring`
const substring = `his`
string.indexOf(substring) !== -1 
// => true
4) Simplest RegExp constructor:
const string = `Let's search this string for a substring`
const expr = /his/  // important: do not use quotes here
expr.test(string) 
// => true
5) .search returns the index of first found, otherwise -1:
const string = `Let's search this string for a substring`
const expr = "/sea/" // <-- note the quotes! You can do plenty magic here
string.search(expr)
// => 14
All these achieve the same thing, but perfomance may vary on large data manipulation.