Compress string: ABBCCCD -> AB2C3D

compressString.js

function compressString(str) {

    // regexp
    const zip = str.replace(/(.)\1{0,}/g, 
        group => (group[0] + (group.length > 1 ? group.length : '')));
    return zip;
}
const str = 'AVVVBBBVVXDHJFFFFDDDDDDHAAAAJJJDDSLSSSDDDD';
console.info("Compression of string: ", compressString(str));