typecheck.js

// a code snippets from underscore.js for type checking in JavaScript

_.each(['Arguments', 'Function', 'String', 'Number', 'Date', 'RegExp', 'Error'], function(name) {
  _['is' + name] = function(obj) {
    return toString.call(obj) === '[object ' + name + ']';
  };
});

function isObject(item) {
  const type = typeof item
  // careful that typeof null === 'object'
  return type === 'object' && !!item || type === 'function'
}