code: function strlen(str) {
    // Call the native functions if there's no surrogate char
    if (!hasSurrogateUnit(str)) {
      return str.length;
    }
  
    let len = 0;
    for (let pos = 0; pos < str.length; pos += getUTF16Length(str, pos)) {
      len++;
    }
    return len;
  }
docs: Fully Unicode-enabled replacement for String#length
  
  @param {string} str  Valid Unicode string
  @return {number}     The number of Unicode characters in the string