How to check if a string contains a substring or not in JavaScript?

Published on 2021-08-08, by Javed Shaikh

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Sometimes when you are building an app in JavaScript, you may come across a situation where you would like to check if a string contains a substring or not. Thankfully we have inbuilt functions to do this job. There are two methods in JavaScript to find if a string contains another string or not such as includes() and indexOf() methods.

The includes() method returns true or false after a search and indexOf() method returns index of a string or -1 if it does not find a match.

Here we will learn about two such methods with examples and see how they work.

  • includes ()
  • indexOf()

String.prototype.includes()

This method checks calling string and performs a scan to see if it contains the another string.This method returns either true or false. If a match is found, it returns true else it returns false. The search performed is case sensitive.

  • It performs case sensitive search
  • It returns true if match is found else it returns false
  • It may not be available in all browsers as it was added in ECMAScript 2015
  • It also has second optional argument i.e index/position where the search should begin. default is 0 (from beginning)

EXAMPLE

javascript
1const quote = “Heaven is under our feet as well as over our heads.”; 2const text = “feet”; 3 4console.log(quote.includes(text)) //true 5console.log(quote.includes("heaven")) //false due case sensitive search 6console.log(quote.includes("Heaven",15)) //false 7console.log(quote.includes("Heaven")) //true 8 9//below snippet prints "found a match" 10if(quote.includes("heads")){ 11 console.log("found a match") 12} 13 14else{ 15 console.log("not found") 16} 17

String.prototype.indexOf()

This method performs a search to check if a string contains another string and returns its index if a match is found. If it does not find a match then it returns -1. This method also does case sensitive search.

  • This method also performs case sensitive search
  • It returns index of first a sub-string on its first occurrence
  • It returns -1 if no match is found
  • It also has second optional argument i.e. index from where the search should begin.

EXAMPLE

javascript
1const quote = "A weed is no more than a flower in disguise." 2 3console.log(quote.indexOf("weed")) //2 4console.log(quote.indexOf("weed",3)) //-1 5console.log(quote.indexOf("tree")) //-1 6console.log(quote.indexOf("flower")) //25 7console.log(quote.indexOf("Flower")) //-1 8console.log(quote.indexOf("disguise",25)) //35

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About the Author

I am a Backend System Engineer at a credit card company, specializing in C/C++ and assembler on IBM's TPF OS. I have a passion for web development and enjoy working with Node.js and Python in my free time.

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