Better way to get type of a Javascript variable

Question

Is there a better way to get the type of a variable in JS than typeof  It works fine when you do    gt  typeof 1  number   gt  typeof  hello   string    But it s useless when you try    gt  typeof  1 2   object   gt r   new RegExp           gt  typeof r  function    I know of instanceof  but this requires you to know the type beforehand        gt   1 2  instanceof Array true  gt  r instanceof RegExp true   Is there a better way

User · Accepted Answer

Angus Croll recently wrote an interesting blog post about this -

http://javascriptweblog.wordpress.com/2011/08/08/fixing-the-javascript-typeof-operator/

He goes through the pros and cons of the various methods then defines a new method 'toType' -

var toType = function(obj) {
  return ({}).toString.call(obj).match(/\s([a-zA-Z]+)/)[1].toLowerCase()
}

User · Answer

This version is a more complete one  const typeOf   obj   gt      let type        toString call obj  match   s  a-zA-Z      1    if  type      Object         const results       function class  s   w     exec obj constructor toString        type    results  amp  amp  results length  gt  2    results 2             return type toLowerCase      Now not only you can have these results   as they ve been answered here  undefined or empty - gt  undefined null - gt  null NaN - gt  number 5 - gt  number    - gt  object    - gt  array    - gt  string function       - gt  function  a  - gt  regexp new Date   - gt  date new Error - gt  error Promise resolve   - gt  promise function        - gt  generatorfunction new WeakMap   - gt  weakmap new Map   - gt  map  But also you can get the type of every instance or object you construct from classes or functions   which is not valid between other answers  all of them return object  class C     constructor         this a   1        function F       this b    Foad     typeOf new C       - gt  c typeOf new F       - gt  f

User · Answer

A reasonably good type capture function is the one used by YUI3   var TYPES          undefined            undefined        number               number        boolean              boolean        string               string         object Function     function         object RegExp       regexp         object Array        array         object Date         date         object Error        error     TOSTRING   Object prototype toString   function type o        return TYPES typeof o     TYPES TOSTRING call o       o    object     null         This captures many of the primitives provided by javascript  but you can always add more by modifying the TYPES object  Note that typeof HTMLElementCollection in Safari will report function  but type HTMLElementCollection  will return object

User · Answer

I guess the most universal solution here - is to check for undefined and null first  then just call constructor name toLowerCase     const getType   v   gt    v     undefined        undefined        v     null          null          v constructor name toLowerCase        console log getType undefined        undefined  console log getType null        null  console log getType           string  console log getType           array  console log getType           object  console log getType new Set          set  console log getType Promise resolve          promise  console log getType new Map          map

User · Answer

typeof condition is used to check variable type  if you are check variable type in if-else condition e g   if typeof Varaible Name  undefined

User · Answer

You can try using constructor name      constructor name new RegExp   constructor name   As with everything JavaScript  someone will eventually invariably point that this is somehow evil  so here is a link to an answer that covers this pretty well   An alternative is to use Object prototype toString call  Object prototype toString call     Object prototype toString call

User · Answer

My 2    Really  part of the reason I m throwing this up here  despite the long list of answers  is to provide a little more all in one type solution and get some feed back in the future on how to expand it to include more real types   With the following solution  as aforementioned  I combined a couple of solutions found here  as well as incorporate a fix for returning a value of jQuery on jQuery defined object if available  I also append the method to the native Object prototype  I know that is often taboo  as it could interfere with other such extensions  but I leave that to user beware  If you don t like this way of doing it  simply copy the base function anywhere you like and replace all variables of this with an argument parameter to pass in  such as arguments 0       function          Object realType     function realType toLower            var r   typeof this          try               if  window hasOwnProperty  jQuery    amp  amp  this constructor  amp  amp  this constructor    jQuery  r    jQuery               else r   this constructor  amp  amp  this constructor name   this constructor name   Object prototype toString call this  slice 8  -1                     catch e    if  this  toString    r   this toString   slice 8  -1             return  toLower   r   r toLowerCase              Object  defineProperty    amp  amp   Object prototype hasOwnProperty  realType             Object defineProperty Object prototype   realType     value  realType      Object prototype  realType     realType          Then simply use with ease  like so   obj realType        would return  Object  obj realType true       would return  object       Note  There is 1 argument passable  If is bool of true  then the return will always be in lowercase    More Examples   true realType                                    Boolean  var a   4  a realType                            Number     div first   realType                          jQuery  document createElement  div   realType           HTMLDivElement    If you have anything to add that maybe helpful  such as defining when an object was created with another library  Moo  Proto  Yui  Dojo  etc     please feel free to comment or edit this and keep it going to be more accurate and precise  OR roll on over to the GitHub I made for it and let me know  You ll also find a quick link to a cdn min file there

User · Answer

You can apply Object prototype toString to any object   var toString   Object prototype toString   console log toString call         - gt   object Array   console log toString call  reg g      - gt   object RegExp   console log toString call         - gt   object Object    This works well in all browsers  with the exception of IE - when calling this on a variable obtained from another window it will just spit out  object Object

User · Answer

Also we can change a little example from ipr101  Object prototype toType   function       return      toString call this  match   s  a-zA-Z      1  toLowerCase       and call as   aaa  toType        string

User · Answer

function getType obj        if obj  amp  amp  obj constructor  amp  amp  obj constructor name            return obj constructor name            return Object prototype toString call obj  slice 8  -1  toLowerCase        In my preliminary tests  this is working pretty well  The first case will print the name of any object created with  new   and the 2nd case should catch everything else   I m using  8  -1  because I m assuming that the result is always going to start with  object and end with   but I m not certain that s true in every scenario

User · Answer

one line function   function type obj        return Object prototype toString call obj  replace     object            1   toLowerCase       this give the same result as jQuery type

User · Answer

You may find the following function useful  function typeOf obj      return    toString call obj  split      1  slice 0  -1  toLowerCase       Or in ES7  comment if further improvements  const   toString     Object prototype   function typeOf obj      const stringified   obj  toString      const type   stringified split      1  slice 0  -1            return type toLowerCase       Results  typeOf      undefined typeOf null     null typeOf NaN     number typeOf 5     number typeOf        object typeOf        array typeOf        string typeOf function           function typeOf  a     regexp typeOf new Date      date typeOf new Error    error typeOf Promise resolve      promise typeOf function           generatorfunction typeOf new WeakMap      weakmap typeOf new Map      map typeOf async function         asyncfunction  Thanks  johnrees for notifying me of  error  promise  generatorfunction

[javascript] Better way to get type of a Javascript variable?

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