How to split string when the value changes in JavaScript?

To split a string when the character value changes in JavaScript, you can use the match() method with a regular expression that captures consecutive identical characters.

Syntax

string.match(/(.)\1*/g)

How the Regular Expression Works

The pattern /(.)\1*/g breaks down as:

• (.) - Captures any single character
• \1 - Matches the same character as captured in group 1
• * - Matches zero or more of the preceding element
• g - Global flag to find all matches

Example

var originalString = "JJJJOHHHHNNNSSSMMMIIITTTTHHH";
var regularExpression = /(.)\1*/g;

console.log("The original string = " + originalString);
var splitting = originalString.match(regularExpression);
console.log("After splitting the original string:");
console.log(splitting);

The original string = JJJJOHHHHNNNSSSMMMIIITTTTHHH
After splitting the original string:
[
  'JJJJ', 'O',
  'HHHH', 'NNN',
  'SSS', 'MMM',
  'III', 'TTTT',
  'HHH'
]

Additional Examples

// Example with numbers
var numberString = "11122233344455";
var numberGroups = numberString.match(/(.)\1*/g);
console.log("Number groups:", numberGroups);

// Example with mixed characters
var mixedString = "aabbccddeeff";
var mixedGroups = mixedString.match(/(.)\1*/g);
console.log("Mixed groups:", mixedGroups);

Number groups: [ '111', '222', '333', '444', '55' ]
Mixed groups: [ 'aa', 'bb', 'cc', 'dd', 'ee', 'ff' ]

Alternative Approach Using Loop

function splitOnChange(str) {
    if (!str) return [];
    
    var result = [];
    var currentGroup = str[0];
    
    for (var i = 1; i < str.length; i++) {
        if (str[i] === str[i - 1]) {
            currentGroup += str[i];
        } else {
            result.push(currentGroup);
            currentGroup = str[i];
        }
    }
    result.push(currentGroup);
    return result;
}

var testString = "AAABBBCCDDD";
console.log("Using loop method:", splitOnChange(testString));

Using loop method: [ 'AAA', 'BBB', 'CC', 'DDD' ]

Conclusion

The match() method with regex /(.)\1*/g provides the most concise way to split strings when character values change. The loop approach offers more control for complex splitting logic.