The most accurate way to check JS object s type

Question

The typeof operator doesn t really help us to find the real type of an object   I ve already seen the following code     Object prototype toString apply t      Question   Is it the most accurate way of checking the object s type

User · Answer

Accepted answer is correct  but I like to define this little utility in most projects I build    var types         get   function prop          return Object prototype toString call prop             null     object Null        object     object Object        array     object Array        string     object String        boolean     object Boolean        number     object Number        date     object Date        Used like this   if types get prop     types number         If you re using angular you can even have it cleanly injected   angular constant  types   types

User · Answer

Old question I know  You don t need to convert it  See this function   function getType  oObj         if  typeof oObj      object                    return   oObj     null    Null                Check if it is an alien object  for example created as  world  hello               typeof oObj constructor      function     Object                else return object name  string            oObj constructor name                                 Test simple types  not constructed types      return   typeof oObj      boolean    Boolean                typeof oObj      number    Number                typeof oObj      string    String                typeof oObj      function    Function  false         Examples   function MyObject          Just for example  console log  getType  new String   hello           String console log  getType  new Function                 Function console log  getType                               Object console log  getType                               Array console log  getType  new MyObject                 MyObject  var bTest   false      uAny      Is undefined     fTest  function            Non constructed standard types console log  getType  bTest                        Boolean console log  getType  1 00                         Number console log  getType  2000                         Number console log  getType   hello                       String console log  getType   hello                       String console log  getType  fTest                        Function console log  getType  uAny                         false  cannot produce                                                    a string   Low cost and simple

User · Answer

I put together a little type check utility inspired by the above correct answers   thetypeof   function name            let obj               obj object    object Object          obj array    object Array          obj string    object String          obj boolean    object Boolean          obj number    object Number          obj type   Object prototype toString call name  slice 1  -1          obj name   Object prototype toString call name  slice 8  -1          obj is    ofType    gt                ofType   ofType toLowerCase                return  obj type     obj ofType    true  false                   obj isnt    ofType    gt                ofType   ofType toLowerCase                return  obj type     obj ofType    true  false                   obj error    ofType    gt                throw new TypeError  The type of   name  is   obj name                   it should be of type   ofType                      return obj           example   if  thetypeof prop  isnt  String    thetypeof prop  error  String   if  thetypeof prop  is  Number       do something

User · Answer

The JavaScript specification gives exactly one proper way to determine the class of an object   Object prototype toString call t     http   bonsaiden github com JavaScript-Garden  types

User · Answer

I d argue that most of the solutions shown here suffer from being over-engineerd  Probably the most simple way to check if a value is of type  object Object  is to check against the  constructor property of it   function isObject  a    return a    null  amp  amp  a constructor     Object      or even shorter with arrow-functions   const isObject   a   gt  a    null  amp  amp  a constructor     Object    The a    null part is necessary because one might pass in null or undefined and you cannot extract a constructor property from either of these   It works with any object created via    the Object constructor literals      Another neat feature of it  is it s ability to give correct reports for custom classes which make use of Symbol toStringTag  For example   class MimicObject     get  Symbol toStringTag          return  Object           The problem here is that when calling Object prototype toString on an instance of it  the false report  object Object  will be returned   let fakeObj   new MimicObject    Object prototype toString call fakeObj      - gt   object Object    But checking against the constructor gives a correct result   let fakeObj   new MimicObject    fakeObj constructor     Object     - gt  false

User · Answer

The best way to find out the REAL type of an object  including BOTH the native Object or DataType name  such as String  Date  Number    etc  AND the REAL type of an object  even custom ones   is by grabbing the name property of the object prototype s constructor   Native Type Ex1   var string1    Test   console log string1   proto   constructor name     displays   String   Ex2   var array1       console log array1   proto   constructor name     displays   Array   Custom Classes    x000D   x000D  function CustomClass    x000D    console log  Custom Class Object Created     x000D    x000D  var custom1   new CustomClass    x000D   x000D  console log custom1   proto   constructor name   x000D   x000D   x000D    displays   CustomClass

User · Answer

var o       var proto    Object getPrototypeOf o   proto     SomeThing    Keep a handle on the prototype you expect the object to have  then compare against it   for example  var o    someString   var proto    Object getPrototypeOf o   proto     String prototype     true

User · Answer

the Object prototype toString is a good way  but its performance is the worst   http   jsperf com check-js-type    Use typeof to solve some basic problem String  Number  Boolean     and use Object prototype toString to solve something complex like Array  Date  RegExp    and this is my solution   var type    function global        var cache           return function obj            var key          return obj     null    null     null               obj     global    global     window in browser or global in nodejs                key   typeof obj       object    key    basic  string  boolean  number  undefined  function               obj nodeType    object     DOM element               cache key        toString call obj      cached  date  regexp  error  object  array  math                 cache key    key slice 8  -1  toLowerCase        get XXXX from  object XXXX   and cache it          this      use as   type function          - gt   function  type  1  2  3       - gt   array  type new Date        - gt   date  type         - gt   object

User · Answer

The best solution is toString  as stated above   function getRealObjectType obj       string       return Object prototype toString call obj  match     w    w       1  toLowerCase        FAIR WARNING  toString considers NaN a number so you must manually safeguard later with Number isNaN value   The other solution suggested  using Object getPrototypeOf fails with null and undefined

[javascript] The most accurate way to check JS object's type?

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