Helper functions to assess if a string is valid or invalid, and if it matches a particular type or not

ifValid.js

function ifValid(str)
{
  if(str !== "" && str !== 0 && str !== '0' && str !== false && str !== 'false' && str !== 'undefined' && str !== undefined && str !== null)
  {
    return true;
  }
  else
  {
    return false;
  }
}

function ifInvalid(str)
{
  if(str === "" || str === 0 || str === '0' || str === false || str === 'false' || str === 'undefined' || str === undefined || str === null)
  {
    return true;
  }
  else
  {
    return false;
  }
}

// Requires checkType fn
function ifType(obj, type)
{
  var obj = obj,
      type = type,
      check = checkType;
  
  if(check(obj) === type)
  {
    return true;
  }
  else
  {
    return false;
  }
}

// Requires checkType fn
function ifNotType(obj, type)
{
  var obj = obj,
      type = type,
      check = checkType;
  
  if(check(obj) !== type)
  {
    return true;
  }
  else
  {
    return false;
  } 
}

function checkType(obj)
{
  var type = Object.prototype.toString.call(obj);
  switch(type)
  {
    case '[object Number]':
      return 'number';
    case '[object String]':
      return 'string';
    case '[object Boolean]':
      return 'boolean';
    case '[object RegExp]':
      return 'regexp';
    case '[object Function]':
      return 'function';
    case '[object Array]':
      return 'array';
    case '[object Object]':
      return 'object';
    case '[object Date]':
      return 'date';
    case '[object Math]':
      return 'math';
    case '[object Null]':
      return 'null';
    case '[object Undefined]':
      return 'undefined';
    case '[object global]':
      return 'global';
    default:
      return false;
  }
}

Please do not use directly in production, modify and then use - as the ifValid and ifInvalid functions are opinionated to suit a particular use case