code: function camelCase(str, { upperCase = false } = {}) {
    if (str.length === 0) {
      return str;
    }
  
    if (upperCase && isAllUpperCaseSnakeCase(str)) {
      // Only convert to lower case if the string is all upper
      // case snake_case. This allowes camelCase strings to go
      // through without changing.
      str = str.toLowerCase();
    }
  
    let out = str[0];
  
    for (let i = 1, l = str.length; i < l; ++i) {
      const char = str[i];
      const prevChar = str[i - 1];
  
      if (char !== '_') {
        if (prevChar === '_') {
          out += char.toUpperCase();
        } else {
          out += char;
        }
      }
    }
  
    return out;
  }
docs: snake_case to camelCase converter that simply reverses the actions done by `snakeCase` function.