snake_case.js

const snakeCase = value => {
  const regex = /[A-Z][^A-Z]+/g;
  const withoutSpaces = value.trim().replace(/\s+/g, '_');
  
  const caps = withoutSpaces.match(regex);
  const splits = withoutSpaces.split(regex);
  
  let finalString = splits.shift();
  
  for (let i = 0; i < splits.length; i++) {
    finalString += `${caps[i]}_${splits[i]}_`;
  }
  
  return finalString
    .toLowerCase()
    .replace(/_+/g, '_')
    .replace(/^_?(.+?)_?$/, '$1');
}