How to get nth occurrence of a string in JavaScript ?
Last Updated : 15 Jul, 2024
In this article, the task is to get the nth occurrence of a substring in a string with the help of JavaScript. We have many methods to do this some of which are described below:
Approaches to get the nth occurrence of a string:
Approach 1: Using split() and join() methods
- First, split the string into sub-strings using the split() method by passing the index also.
- Again join the substrings on the passed substring using join() method.
- Returns the index of the nth occurrence of the string.
Example: In this example, the split() and join() methods are used to get the index of a substring.
JavaScript // Input string let string = "Geeks gfg Geeks Geek Geeks gfg"; // String to search let searchString = "Geeks"; // occurrence number let occurrence = 3; console.log( occurrence + "rd occurrence of a '" + searchString + "' in " + string + "'." ); // Function to get index of occurrence function getPos(str, subStr, i) { return str.split(subStr, i).join(subStr).length; } function GFG_Fun() { console.log(getPos( string, searchString, occurrence )); } GFG_Fun(); Output3rd occurrence of a 'Geeks' in Geeks gfg Geeks Geek Geeks gfg'. 21
Approach 2: Using indexOf() method
Go through each substring one by one and return the index of the last substring. This approach uses the indexOf() method to return the index of the nth occurrence of the string.
Example: This example uses the indexOf() method to find the index of a substring.
JavaScript // Input string let string = "Geeks gfg Geeks Geek Geeks gfg"; // String to search let searchString = "Geeks"; // occurrence number let occurrence = 3; console.log( occurrence + "rd occurrence of a '" + searchString + "' in " + string + "'." ); // Function to get index of occurrence function getIndex(str, substr, ind) { let Len = str.length, i = -1; while (ind-- && i++ < Len) { i = str.indexOf(substr, i); if (i < 0) break; } return i; } function GFG_Fun() { console.log(getIndex(string, searchString, occurrence)); } GFG_Fun(); Output3rd occurrence of a 'Geeks' in Geeks gfg Geeks Geek Geeks gfg'. 21
Approach 3: Using regular expressions
Regular expressions offer a powerful way to search for patterns within strings. We can leverage the exec() method along with a regular expression to find the nth occurrence of a substring.
Example:
JavaScript // Input string let string = "Geeks gfg Geeks Geek Geeks gfg"; // String to search let searchString = "Geeks"; // occurrence number let occurrence = 3; // Create a regular expression with global flag to find all occurrences let regex = new RegExp(searchString, 'g'); let matches = Array.from(string.matchAll(regex)); // Check if nth occurrence exists if(matches.length >= occurrence) { let nthIndex = matches[occurrence - 1].index; console.log(occurrence + "rd occurrence of a '" + searchString + "' in " + string + "'."); console.log("Index of the " + occurrence + "rd occurrence: " + nthIndex); } else { console.log("The string does not have " + occurrence + " occurrences of '" + searchString + "'."); } Output3rd occurrence of a 'Geeks' in Geeks gfg Geeks Geek Geeks gfg'. Index of the 3rd occurrence: 21
Approach 4: Using lastIndexOf() Method in a Loop
This approach utilizes the lastIndexOf() method in a loop to find the nth occurrence of a substring from the end of the string. This method is particularly useful when you want to search from the end of the string backwards.
Example:
JavaScript // Input string let string = "Geeks gfg Geeks Geek Geeks gfg"; // String to search let searchString = "Geeks"; // occurrence number let occurrence = 3; console.log( occurrence + "rd occurrence of a '" + searchString + "' in " + string + "'." ); // Function to get index of occurrence function getLastIndex(str, substr, occ) { let index = str.length; while (occ-- > 0 && index >= 0) { index = str.lastIndexOf(substr, index - 1); } return index; } function GFG_Fun() { console.log(getLastIndex(string, searchString, occurrence)); } GFG_Fun(); Output3rd occurrence of a 'Geeks' in Geeks gfg Geeks Geek Geeks gfg'. 0
Approach 5: Using a Loop and substr()
This approach involves using a simple loop to iterate through the string and find the nth occurrence of a substring. By keeping track of the current position and searching for the substring using the indexOf() method, we can determine the nth occurrence.
Example:
JavaScript function getNthOccurrence(string, substring, n) { let count = 0; let position = 0; while (count < n) { position = string.indexOf(substring, position); if (position === -1) { return -1; } count++; position++; } return position - 1; } const str = "the quick brown fox jumps over the lazy dog. the dog barks."; const subStr = "the"; const nth = 2; const result = getNthOccurrence(str, subStr, nth); console.log(result); Approach 6: Using Array.prototype.reduce() Method
In this approach, we utilize the reduce() method to traverse the string and keep track of the occurrences of the substring. This method provides a functional programming alternative to loops and maintains the current position and count of occurrences to find the nth occurrence of the substring.
Example:
JavaScript function getNthOccurrence(str, subStr, n) { let count = 0; let result = str.split(subStr).reduce((acc, part, index, array) => { if (index < array.length - 1) { count++; if (count === n) { acc = acc.length + part.length; } return acc + part + subStr; } return acc + part; }, ''); return count >= n ? result.length - subStr.length : -1; } let str = "This is a test. This test is for testing."; let subStr = "test"; let nth = 2; console.log(getNthOccurrence(str, subStr, nth)); // Output: 25
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