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

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

const quote = “Heaven is under our feet as well as over our heads.”;
const text = “feet”;

console.log(quote.includes(text))     //true
console.log(quote.includes("heaven")) //false due case sensitive search
console.log(quote.includes("Heaven",15))  //false
console.log(quote.includes("Heaven"))     //true

//below snippet prints "found a match"
if(quote.includes("heads")){
  console.log("found a match")
}

else{
  console.log("not found")
}

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

const quote = "A weed is no more than a flower in disguise."

console.log(quote.indexOf("weed"))        //2
console.log(quote.indexOf("weed",3))      //-1
console.log(quote.indexOf("tree"))        //-1
console.log(quote.indexOf("flower"))      //25
console.log(quote.indexOf("Flower"))      //-1
console.log(quote.indexOf("disguise",25)) //35

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