Checking whether or not a string contains another string, or just a single
character. It’s a been a pretty unavoidable conditional check in my programming career. It’s not quite a problem for the ages, but it comes up regularly and can be approached a few different ways.
ES5 and prior
indexOf
Ahhhhh indexOf. It can tell you if an array contains a value or whether or
not a string contains another string. You won’t receive a boolean from this
method, since it it used to detect the position of the first instance or -1
when the value isn’t found. Fortunately we can just cast the value as a boolean:
const haystack = 'This is my amazing string'
const needle = 'amazing'
const hasNeedle = !!(haystack.indexOf(needle) > -1
RegExp
Good ol’ RegExp. Often times frowned upon due to speed implications. With
modern JavaScript, RegExp is quite performant and comes with a handful of
methods that could leveraged to check if a string contains another string. The
most basic of these methods is RegExp.test() which simply tests whether or not
a string passes the regular expression:
const haystack = 'This is my amazing string'
const needle = new RegExp('amazing' // or simply /amazing/
const hasNeedle = needle.test(haystack
Using regular expressions has the added bonus of being able to do case
insensitive searches:
const haystack = 'This is my amazing string'
const needle = new RegExp('amazing', 'i' // or simply /amazing/i
const hasNeedle = needle.test(haystack
ES6
Granted, all of the aforementioned methods still work here in the modern world,
but if you are able to leverage ES6, why wouldn’t you?
includes
Similar to indexOf, includes is one of those methods that can work with both
arrays and strings (yes, strings are technically arrays). The advantage to using
includes is that it returns a boolean value meaning that it’s been designed
more for our use case of finding a string in another string:
const haystack = 'This is my amazing string'
const needle = 'amazing'
const hasNeedle = haystack.includes(needle
But sadly, includes doesn’t support case insensitive searches, so if that’s a
requirement ES6 has to take the back burner.
