const regex = /^[a-z0-9](?=[a-z0-9 ]{0,49}$)(?=([a-z0-9]+(?: [a-z0-9]+)*))\1$/gmi;
// Alternative syntax using RegExp constructor
// const regex = new RegExp('^[a-z0-9](?=[a-z0-9 ]{0,49}$)(?=([a-z0-9]+(?: [a-z0-9]+)*))\\1$', 'gmi')
const str = `abcdefghij abcdefghij abcdefghij abcdefghij abcdef
abcdefghij abcdefghij abcdefghij abcdefghij abcdef
ghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjh4 j kljlkjkljkljlk lkjlk j lk jkjlkjklljljghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjh4 j kljlkjkljkljlk lkjlk j lk jkjlkjklljljghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjh4 j kljlkjkljkljlk lkjlk j lk jkjlkjklljljghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjh4 j kljlkjkljkljlk lkjlk j lk jkjlkjklljljghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjh4 j kljlkjkljkljlk lkjlk j lk jkjlkjklljljghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjh4 j kljlkjkljkljlk lkjlk j lk jkjlkjklljljghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjh4 j kljlkjkljkljlk lkjlk j lk jkjlkjklljljghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjh4 j kljlkjkljkljlk lkjlk j lk jkjlkjklljlj
ghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjh4&
ghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjghgffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffkljlkjh4
@\$%
@\$% #\$%
a @#\$% 2
`;
// Reset `lastIndex` if this regex is defined globally
// regex.lastIndex = 0;
let m;
while ((m = regex.exec(str)) !== null) {
// This is necessary to avoid infinite loops with zero-width matches
if (m.index === regex.lastIndex) {
regex.lastIndex++;
}
// The result can be accessed through the `m`-variable.
m.forEach((match, groupIndex) => {
console.log(`Found match, group ${groupIndex}: ${match}`);
});
}
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for JavaScript, please visit: https://developer.mozilla.org/en/docs/Web/JavaScript/Guide/Regular_Expressions