How do I enumerate the properties of a JavaScript object

Question

How do I enumerate the properties of a JavaScript object   I actually want to list all the defined variables and their values  but I ve learned that defining a variable actually creates a property of the window object

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If you re trying to enumerate the properties in order to write new code against the object  I would recommend using a debugger like Firebug to see them visually    Another handy technique is to use Prototype s Object toJSON   to serialize the object to JSON  which will show you both property names and values    var data    name   Violet   occupation   character   age  25  pets    frog    rabbit     Object toJSON data     - gt     name    Violet    occupation    character    age   25   pets     frog   rabbit       http   www prototypejs org api object tojson

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Python s dict has  keys  method  and that is really useful  I think in JavaScript we can have something this   function keys        var k           for var p in this            if this hasOwnProperty p               k push p             return k    Object defineProperty Object prototype   keys     value   keys  enumerable false       EDIT  But the answer of  carlos-ruana works very well  I tested Object keys window   and the result is what I expected   EDIT after 5 years  it is not good idea to extend Object  because it can conflict with other libraries that may want to use keys on their objects and it will lead unpredictable behavior on your project   carlos-ruana answer is the correct way to get keys of an object

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Python s dict has  keys  method  and that is really useful  I think in JavaScript we can have something this   function keys        var k           for var p in this            if this hasOwnProperty p               k push p             return k    Object defineProperty Object prototype   keys     value   keys  enumerable false       EDIT  But the answer of  carlos-ruana works very well  I tested Object keys window   and the result is what I expected   EDIT after 5 years  it is not good idea to extend Object  because it can conflict with other libraries that may want to use keys on their objects and it will lead unpredictable behavior on your project   carlos-ruana answer is the correct way to get keys of an object

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Simple JavaScript code   for var propertyName in myObject          propertyName is what you want        You can get the value like this  myObject propertyName      jQuery   jQuery each obj  function key  value          key is what you want        The value is in  value

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Here s how to enumerate an object s properties   var params     name   myname   age   myage     for  var key in params      alert key         params key

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You can use the for of loop   If you want an array use    Object keys object1   Ref  Object keys

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Here s how to enumerate an object s properties   var params     name   myname   age   myage     for  var key in params      alert key         params key

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I found it    for  property in object       do stuff   will list all the properties  and therefore all the globally declared variables on the window object

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If you are using the Underscore js library  you can use function keys     keys  one   1  two   2  three   3      gt    one    two    three

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Simple enough   for var propertyName in myObject          propertyName is what you want       you can get the value like this  myObject propertyName      Now  you will not get private variables this way because they are not available     EDIT   bitwiseplatypus is correct that unless you use the hasOwnProperty   method  you will get properties that are inherited - however  I don t know why anyone familiar with object-oriented programming would expect anything less  Typically  someone that brings this up has been subjected to Douglas Crockford s warnings about this  which still confuse me a bit  Again  inheritance is a normal part of OO languages and is therefore part of JavaScript  notwithstanding it being prototypical   Now  that said  hasOwnProperty   is useful for filtering  but we don t need to sound a warning as if there is something dangerous in getting inherited properties   EDIT 2   bitwiseplatypus brings up the situation that would occur should someone add properties methods to your objects at a point in time later than when you originally wrote your objects  via its prototype  - while it is true that this might cause unexpected behavior  I personally don t see that as my problem entirely  Just a matter of opinion  Besides  what if I design things in such a way that I use prototypes during the construction of my objects and yet have code that iterates over the properties of the object and I want all inherited properties  I wouldn t use hasOwnProperty    Then  let s say  someone adds new properties later  Is that my fault if things behave badly at that point  I don t think so  I think this is why jQuery  as an example  has specified ways of extending how it works  via jQuery extend and jQuery fn extend

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The standard way  which has already been proposed several times is   for  var name in myObject      alert name       However Internet Explorer 6  7 and 8 have a bug in the JavaScript interpreter  which has the effect that some keys are not enumerated  If you run this code   var obj     toString  12   for  var name in obj      alert name       If will alert  12  in all browsers except IE  IE will simply ignore this key  The affected key values are    isPrototypeOf hasOwnProperty toLocaleString toString valueOf   To be really safe in IE you have to use something like   for  var key in myObject      alert key      var shadowedKeys        isPrototypeOf      hasOwnProperty      toLocaleString      toString      valueOf     for  var i 0  a shadowedKeys  l a length  i lt l  i        if map hasOwnProperty a i          alert a i            The good news is that EcmaScript 5 defines the Object keys myObject  function  which returns the keys of an object as array and some browsers  e g  Safari 4  already implement it

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I m still a beginner in JavaScript  but I wrote a small function to recursively print all the properties of an object and its children   getDescription object  tabs      var str      n     for  var x in object          str    Array tabs   2  join   t     x               if  typeof object x       object   amp  amp  object x             str    this getDescription object x   tabs   1           else           str    object x                 str      n         str    Array tabs   1  join   t            return str

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for  prop in obj        alert prop           obj prop

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I think an example of the case that has caught me by surprise is relevant   var myObject     name   Cody   status   Surprised     for  var propertyName in myObject      document writeln  propertyName           myObject propertyName         But to my surprise  the output is  name   Cody status   Surprised forEach   function  obj  callback        for  prop in obj            if  obj hasOwnProperty prop   amp  amp  typeof obj prop       function                 callback prop                       Why  Another script on the page has extended the Object prototype   Object prototype forEach   function  obj  callback      for   prop in obj         if   obj hasOwnProperty  prop    amp  amp  typeof obj prop       function            callback  prop

User · Answer

If you re trying to enumerate the properties in order to write new code against the object  I would recommend using a debugger like Firebug to see them visually    Another handy technique is to use Prototype s Object toJSON   to serialize the object to JSON  which will show you both property names and values    var data    name   Violet   occupation   character   age  25  pets    frog    rabbit     Object toJSON data     - gt     name    Violet    occupation    character    age   25   pets     frog   rabbit       http   www prototypejs org api object tojson

User · Answer

Simple enough   for var propertyName in myObject          propertyName is what you want       you can get the value like this  myObject propertyName      Now  you will not get private variables this way because they are not available     EDIT   bitwiseplatypus is correct that unless you use the hasOwnProperty   method  you will get properties that are inherited - however  I don t know why anyone familiar with object-oriented programming would expect anything less  Typically  someone that brings this up has been subjected to Douglas Crockford s warnings about this  which still confuse me a bit  Again  inheritance is a normal part of OO languages and is therefore part of JavaScript  notwithstanding it being prototypical   Now  that said  hasOwnProperty   is useful for filtering  but we don t need to sound a warning as if there is something dangerous in getting inherited properties   EDIT 2   bitwiseplatypus brings up the situation that would occur should someone add properties methods to your objects at a point in time later than when you originally wrote your objects  via its prototype  - while it is true that this might cause unexpected behavior  I personally don t see that as my problem entirely  Just a matter of opinion  Besides  what if I design things in such a way that I use prototypes during the construction of my objects and yet have code that iterates over the properties of the object and I want all inherited properties  I wouldn t use hasOwnProperty    Then  let s say  someone adds new properties later  Is that my fault if things behave badly at that point  I don t think so  I think this is why jQuery  as an example  has specified ways of extending how it works  via jQuery extend and jQuery fn extend

User · Answer

If you are using the Underscore js library  you can use function keys     keys  one   1  two   2  three   3      gt    one    two    three

User · Answer

Use a for  in loop to enumerate an object s properties  but be careful  The enumeration will return properties not just of the object being enumerated  but also from the prototypes of any parent objects   var myObject    foo   bar     for  var name in myObject      alert name         results in a single alert of  foo   Object prototype baz    quux    for  var name in myObject      alert name         results in two alerts  one for  foo  and one for  baz    To avoid including inherited properties in your enumeration  check hasOwnProperty     for  var name in myObject      if  myObject hasOwnProperty name         alert name           Edit  I disagree with JasonBunting s statement that we don t need to worry about enumerating inherited properties  There is danger in enumerating over inherited properties that you aren t expecting  because it can change the behavior of your code   It doesn t matter whether this problem exists in other languages  the fact is it exists  and JavaScript is particularly vulnerable since modifications to an object s prototype affects child objects even if the modification takes place after instantiation   This is why JavaScript provides hasOwnProperty    and this is why you should use it in order to ensure that third party code  or any other code that might modify a prototype  doesn t break yours  Apart from adding a few extra bytes of code  there is no downside to using hasOwnProperty

User · Answer

I found it    for  property in object       do stuff   will list all the properties  and therefore all the globally declared variables on the window object

User · Answer

I found it    for  property in object       do stuff   will list all the properties  and therefore all the globally declared variables on the window object

User · Answer

If you re trying to enumerate the properties in order to write new code against the object  I would recommend using a debugger like Firebug to see them visually    Another handy technique is to use Prototype s Object toJSON   to serialize the object to JSON  which will show you both property names and values    var data    name   Violet   occupation   character   age  25  pets    frog    rabbit     Object toJSON data     - gt     name    Violet    occupation    character    age   25   pets     frog   rabbit       http   www prototypejs org api object tojson

User · Answer

Use a for  in loop to enumerate an object s properties  but be careful  The enumeration will return properties not just of the object being enumerated  but also from the prototypes of any parent objects   var myObject    foo   bar     for  var name in myObject      alert name         results in a single alert of  foo   Object prototype baz    quux    for  var name in myObject      alert name         results in two alerts  one for  foo  and one for  baz    To avoid including inherited properties in your enumeration  check hasOwnProperty     for  var name in myObject      if  myObject hasOwnProperty name         alert name           Edit  I disagree with JasonBunting s statement that we don t need to worry about enumerating inherited properties  There is danger in enumerating over inherited properties that you aren t expecting  because it can change the behavior of your code   It doesn t matter whether this problem exists in other languages  the fact is it exists  and JavaScript is particularly vulnerable since modifications to an object s prototype affects child objects even if the modification takes place after instantiation   This is why JavaScript provides hasOwnProperty    and this is why you should use it in order to ensure that third party code  or any other code that might modify a prototype  doesn t break yours  Apart from adding a few extra bytes of code  there is no downside to using hasOwnProperty

User · Answer

Simple JavaScript code   for var propertyName in myObject          propertyName is what you want        You can get the value like this  myObject propertyName      jQuery   jQuery each obj  function key  value          key is what you want        The value is in  value

User · Answer

In modern browsers  ECMAScript 5  to get all enumerable properties you can do   Object keys obj   Check the link to get a snippet for backward compatibility on older browsers   Or to get also non-enumerable properties   Object getOwnPropertyNames obj   Check ECMAScript 5 compatibility table  Additional info  What is a enumerable attribute

User · Answer

I found it    for  property in object       do stuff   will list all the properties  and therefore all the globally declared variables on the window object

User · Answer

for  prop in obj        alert prop           obj prop

User · Answer

The standard way  which has already been proposed several times is   for  var name in myObject      alert name       However Internet Explorer 6  7 and 8 have a bug in the JavaScript interpreter  which has the effect that some keys are not enumerated  If you run this code   var obj     toString  12   for  var name in obj      alert name       If will alert  12  in all browsers except IE  IE will simply ignore this key  The affected key values are    isPrototypeOf hasOwnProperty toLocaleString toString valueOf   To be really safe in IE you have to use something like   for  var key in myObject      alert key      var shadowedKeys        isPrototypeOf      hasOwnProperty      toLocaleString      toString      valueOf     for  var i 0  a shadowedKeys  l a length  i lt l  i        if map hasOwnProperty a i          alert a i            The good news is that EcmaScript 5 defines the Object keys myObject  function  which returns the keys of an object as array and some browsers  e g  Safari 4  already implement it

User · Answer

I think an example of the case that has caught me by surprise is relevant   var myObject     name   Cody   status   Surprised     for  var propertyName in myObject      document writeln  propertyName           myObject propertyName         But to my surprise  the output is  name   Cody status   Surprised forEach   function  obj  callback        for  prop in obj            if  obj hasOwnProperty prop   amp  amp  typeof obj prop       function                 callback prop                       Why  Another script on the page has extended the Object prototype   Object prototype forEach   function  obj  callback      for   prop in obj         if   obj hasOwnProperty  prop    amp  amp  typeof obj prop       function            callback  prop

User · Answer

for  prop in obj        alert prop           obj prop

User · Answer

Simple enough   for var propertyName in myObject          propertyName is what you want       you can get the value like this  myObject propertyName      Now  you will not get private variables this way because they are not available     EDIT   bitwiseplatypus is correct that unless you use the hasOwnProperty   method  you will get properties that are inherited - however  I don t know why anyone familiar with object-oriented programming would expect anything less  Typically  someone that brings this up has been subjected to Douglas Crockford s warnings about this  which still confuse me a bit  Again  inheritance is a normal part of OO languages and is therefore part of JavaScript  notwithstanding it being prototypical   Now  that said  hasOwnProperty   is useful for filtering  but we don t need to sound a warning as if there is something dangerous in getting inherited properties   EDIT 2   bitwiseplatypus brings up the situation that would occur should someone add properties methods to your objects at a point in time later than when you originally wrote your objects  via its prototype  - while it is true that this might cause unexpected behavior  I personally don t see that as my problem entirely  Just a matter of opinion  Besides  what if I design things in such a way that I use prototypes during the construction of my objects and yet have code that iterates over the properties of the object and I want all inherited properties  I wouldn t use hasOwnProperty    Then  let s say  someone adds new properties later  Is that my fault if things behave badly at that point  I don t think so  I think this is why jQuery  as an example  has specified ways of extending how it works  via jQuery extend and jQuery fn extend

User · Answer

Use a for  in loop to enumerate an object s properties  but be careful  The enumeration will return properties not just of the object being enumerated  but also from the prototypes of any parent objects   var myObject    foo   bar     for  var name in myObject      alert name         results in a single alert of  foo   Object prototype baz    quux    for  var name in myObject      alert name         results in two alerts  one for  foo  and one for  baz    To avoid including inherited properties in your enumeration  check hasOwnProperty     for  var name in myObject      if  myObject hasOwnProperty name         alert name           Edit  I disagree with JasonBunting s statement that we don t need to worry about enumerating inherited properties  There is danger in enumerating over inherited properties that you aren t expecting  because it can change the behavior of your code   It doesn t matter whether this problem exists in other languages  the fact is it exists  and JavaScript is particularly vulnerable since modifications to an object s prototype affects child objects even if the modification takes place after instantiation   This is why JavaScript provides hasOwnProperty    and this is why you should use it in order to ensure that third party code  or any other code that might modify a prototype  doesn t break yours  Apart from adding a few extra bytes of code  there is no downside to using hasOwnProperty

User · Answer

If you re trying to enumerate the properties in order to write new code against the object  I would recommend using a debugger like Firebug to see them visually    Another handy technique is to use Prototype s Object toJSON   to serialize the object to JSON  which will show you both property names and values    var data    name   Violet   occupation   character   age  25  pets    frog    rabbit     Object toJSON data     - gt     name    Violet    occupation    character    age   25   pets     frog   rabbit       http   www prototypejs org api object tojson

User · Answer

In modern browsers  ECMAScript 5  to get all enumerable properties you can do   Object keys obj   Check the link to get a snippet for backward compatibility on older browsers   Or to get also non-enumerable properties   Object getOwnPropertyNames obj   Check ECMAScript 5 compatibility table  Additional info  What is a enumerable attribute

User · Answer

Use a for  in loop to enumerate an object s properties  but be careful  The enumeration will return properties not just of the object being enumerated  but also from the prototypes of any parent objects   var myObject    foo   bar     for  var name in myObject      alert name         results in a single alert of  foo   Object prototype baz    quux    for  var name in myObject      alert name         results in two alerts  one for  foo  and one for  baz    To avoid including inherited properties in your enumeration  check hasOwnProperty     for  var name in myObject      if  myObject hasOwnProperty name         alert name           Edit  I disagree with JasonBunting s statement that we don t need to worry about enumerating inherited properties  There is danger in enumerating over inherited properties that you aren t expecting  because it can change the behavior of your code   It doesn t matter whether this problem exists in other languages  the fact is it exists  and JavaScript is particularly vulnerable since modifications to an object s prototype affects child objects even if the modification takes place after instantiation   This is why JavaScript provides hasOwnProperty    and this is why you should use it in order to ensure that third party code  or any other code that might modify a prototype  doesn t break yours  Apart from adding a few extra bytes of code  there is no downside to using hasOwnProperty

User · Answer

for  prop in obj        alert prop           obj prop

User · Answer

Simple enough   for var propertyName in myObject          propertyName is what you want       you can get the value like this  myObject propertyName      Now  you will not get private variables this way because they are not available     EDIT   bitwiseplatypus is correct that unless you use the hasOwnProperty   method  you will get properties that are inherited - however  I don t know why anyone familiar with object-oriented programming would expect anything less  Typically  someone that brings this up has been subjected to Douglas Crockford s warnings about this  which still confuse me a bit  Again  inheritance is a normal part of OO languages and is therefore part of JavaScript  notwithstanding it being prototypical   Now  that said  hasOwnProperty   is useful for filtering  but we don t need to sound a warning as if there is something dangerous in getting inherited properties   EDIT 2   bitwiseplatypus brings up the situation that would occur should someone add properties methods to your objects at a point in time later than when you originally wrote your objects  via its prototype  - while it is true that this might cause unexpected behavior  I personally don t see that as my problem entirely  Just a matter of opinion  Besides  what if I design things in such a way that I use prototypes during the construction of my objects and yet have code that iterates over the properties of the object and I want all inherited properties  I wouldn t use hasOwnProperty    Then  let s say  someone adds new properties later  Is that my fault if things behave badly at that point  I don t think so  I think this is why jQuery  as an example  has specified ways of extending how it works  via jQuery extend and jQuery fn extend

User · Answer

You can use the for of loop   If you want an array use    Object keys object1   Ref  Object keys

User · Answer

I m still a beginner in JavaScript  but I wrote a small function to recursively print all the properties of an object and its children   getDescription object  tabs      var str      n     for  var x in object          str    Array tabs   2  join   t     x               if  typeof object x       object   amp  amp  object x             str    this getDescription object x   tabs   1           else           str    object x                 str      n         str    Array tabs   1  join   t            return str

[javascript] How do I enumerate the properties of a JavaScript object?

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