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How to Check Whether a String Contains a Substring in JavaScript

Topic: JavaScript / jQueryPrev|Next

Answer: Use the indexOf() Method

The simplest and fastest way to check whether a string contains a substring or not in JavaScript is the indexOf() method. This method returns the index or position of the first occurrence of substring within the string, otherwise, it returns -1 if no match found. Here is an example:

  • <script>
  •     // Sample string
  •     var str = "The quick brown fox jumps over the lazy dog."
  •     
  •     // Check if the substring exists inside the string
  •     var index = str.indexOf("fox");    
  •     if(index !== -1){
  •         alert("Substring found!");
  •     } else{
  •         alert("Substring not found!");
  •     }
  • </script>

In ES6 you can use the includes() method to check if a contains a substring. This method simply returns true or false instead of the index. Here's an example:

  • <script>
  •     // Sample string
  •     var str = "The quick brown fox jumps over the lazy dog."
  •     
  •     // Check if string contains substring
  •     if(str.includes("fox")){
  •         alert("Substring found!");
  •     } else{
  •         alert("Substring not found!");
  •     }
  • </script>

Check out the tutorial on JavaScript ES6 features to learn about new features introduced in ES6.

Further, you can use the search() method to search a particular piece of text or pattern (using regular expression) inside a string. Like indexOf() method the search() method also returns the index of the first match, and returns -1 if no matches were found.

  • <script>
  •     // Sample string
  •     var str = "Color red looks brighter than color blue."
  •     
  •     // Search the string for a match
  •     var index = str.search(/color/i);  
  •     if(index !== -1){
  •         alert("Substring found!");
  •     } else{
  •         alert("Substring not found!");
  •     }
  • </script>

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