Creating JS object with Object.create(null)?

111

I know a lot of ways to create JS objects but I didn't know the Object.create(null)'s one.

Question:

is it exactly the same as:

var p = {}

var p2 = Object.create(null);

edited Jul 17 '18 at 22:58

tanguy_k

6,14322939

asked Mar 20 '13 at 8:12

Royi Namir

74.8k98329588

add a comment |

111

I know a lot of ways to create JS objects but I didn't know the Object.create(null)'s one.

Question:

is it exactly the same as:

var p = {}

var p2 = Object.create(null);

edited Jul 17 '18 at 22:58

tanguy_k

6,14322939

asked Mar 20 '13 at 8:12

Royi Namir

74.8k98329588

add a comment |

111

I know a lot of ways to create JS objects but I didn't know the Object.create(null)'s one.

Question:

is it exactly the same as:

var p = {}

var p2 = Object.create(null);

edited Jul 17 '18 at 22:58

tanguy_k

6,14322939

asked Mar 20 '13 at 8:12

Royi Namir

74.8k98329588

I know a lot of ways to create JS objects but I didn't know the Object.create(null)'s one.

Question:

is it exactly the same as:

var p = {}

var p2 = Object.create(null);

javascript

edited Jul 17 '18 at 22:58

tanguy_k

6,14322939

asked Mar 20 '13 at 8:12

Royi Namir

74.8k98329588

edited Jul 17 '18 at 22:58

tanguy_k

6,14322939

asked Mar 20 '13 at 8:12

Royi Namir

74.8k98329588

edited Jul 17 '18 at 22:58

tanguy_k

6,14322939

edited Jul 17 '18 at 22:58

tanguy_k

6,14322939

edited Jul 17 '18 at 22:58

tanguy_k

6,14322939

asked Mar 20 '13 at 8:12

Royi Namir

74.8k98329588

asked Mar 20 '13 at 8:12

Royi Namir

74.8k98329588

asked Mar 20 '13 at 8:12

Royi Namir

74.8k98329588

add a comment |

4 Answers
4

active

oldest

votes

151

I think they are not equivalent. If I'm not mistaking, {}.constructor.prototype == Object.prototype while Object.create(null) doesn't inherit from anywhere and thus has no properties at all.

In other words: A javascript object inherits from Object by default, unless you explicitly create it specifying null as its prototype, as in Object.create(null).

{} would instead be equivalent to Object.create(Object.prototype).

In Chrome Devtool you can see that Object.create(null) have no __proto which {} have.

enter image description here

edited Aug 28 '17 at 11:13

TryingToImprove

3,74011732

answered Mar 20 '13 at 8:37

Peter Herdenborg

4,49011320

add a comment |

They are definitely not equivalent. I'm writing this answer to more fully explain why it makes a difference.

var p = {};

Creates an object that inherits the properties and methods from Object.

var p2 = Object.create(null);

Creates an object that doesn't inherit anything.

If you are using an object as a map, and you create an object using method 1 above, then you have to be extra careful when doing lookups in the map. Because the properties and methods from Object are inherited, your code may run into a case where there are keys in the map that you never inserted. For example, if you did a lookup on toString, you would find a function, even though you never put that value there. You can work around that like this:

if (Object.prototype.hasOwnProperty.call(p, 'toString')) {

    // we actually inserted a 'toString' key into p

}

_{Note that it is fine to assign something to p.toString, it will simply override the inherited toString function on p.}

Note that you can't just do p.hasOwnProperty('toString') because you may have inserted a key "hasOwnProperty" into p, so we force it to use the implementation in Object.

On the other hand, if you use method 2 above, then you won't have to worry about things from Object appearing in the map.

You can't check for the existence of a property with a simple if like this:

// Unreliable:

if (p[someKey]) {

    // ...

}

The value might be an empty string, might be false, or null, or undefined, or 0, or NaN, etc. To check whether a property exists at all, you would still need to use Object.prototype.hasOwnProperty.call(p, someKey).

answered Jan 12 '14 at 19:29

doug65536

5,05413045

3

A simpler alternative for checking for the existence of a property is: if (someKey in p) {

– mrcrowl
Nov 4 '16 at 7:51

2

@mrcrowl Only if they used Object.create(null). I prefer not to make assumptions like that, even if you were absolutely right that it used Object.create(null), the code could change, the object could be replaced with one that inherits Object at some point. hasOwnProperty always works.

– doug65536
Nov 4 '16 at 8:13

1

I feel being careful about something like this should be unnecessary. I appreciate your answer but documentation should give you the api necessary to work with whatever code you're working with. If you're grabbing some random code from github, then you can fork it and be safe from less documented updates. Not to mention {} is so much more prevalent than Object.create(null), that if your code accidentally grabs an inherited property at this point, you likely have way bigger bugs to worry about. I can only see people using Object.create(null) as a minor optimization.

– aaaaaa
Sep 13 '17 at 21:16

Double negation !!p[key] works good with Object.create(null). But hasKey = (key, input) => Object.prototype.hasOwnProperty.call(input, key) is not bad either

– andreid
May 2 '18 at 10:03

> Note that you can't just do p.hasOwnProperty('toString') because you may have inserted a key "hasOwnProperty" into p, so we force it to use the implementation in Object. That's is unnecessary. In this case, you can't use any methods in p because every method could be inserted and so become not safe.

– xianshenglu
Dec 6 '18 at 2:13

|
show 2 more comments

If someone is looking for implementing Object.create(null), just to know how it works. It is written using proto which is non-standard and hence, I do not recommend it.

function objectCreateMimic()

{

  /*optional parameters: prototype_object, own_properties*/

  var P = arguments.length>0?arguments[0]:-1;

  var Q = arguments.length>1?arguments[1]:null;

  var o = {};

  if(P!==null && typeof P === "object")

  {

    o.__proto__ = P;

  }

  else if(P===null)

  {

    o.__proto__ = null;

  }

  if(Q!==null && typeof Q === "object")

  {

   for(var key in Q)

   {

     o[key] = Q[key];

   }

  }

  return o;

}

Note: I wrote this, out of curiosity, and it is only written in simple terms, for instance, I am not transferring the property descriptors from the second object to the return object.

edited Nov 19 '14 at 7:07

answered Nov 19 '14 at 6:51

Aravind

2,50011631

1

Note that as of ECMAScript's release in summer, __proto__ will now officially be part of the language.

– Chiru
Mar 20 '15 at 0:55

1

Why -1 in arguments.length>0?arguments[0]:-1;?

– happy_marmoset
Dec 3 '15 at 9:39

@happy_marmoset late response, but it looks like it's just a non-null placeholder so that the Object prototype is retained if the first argument isn't given. Variable names could be a lot better here.

– Mike Hill
Jul 31 '17 at 0:11

Also, the second parameter should describe the property descriptors rather than the actual properties themselves. See reference here: developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…

– Mike Hill
Jul 31 '17 at 0:16

add a comment |

Creating objects by using {} will create an object whose prototype is Object.prototype which inherits the basic functions from Object prototype while creating objects by using Object.create(null) will create an empty object whose prototype is null.

answered Apr 12 '18 at 19:16

Praveen Kishor

6951716

add a comment |

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4 Answers
4

active

oldest

votes

4 Answers
4

active

oldest

votes

151

I think they are not equivalent. If I'm not mistaking, {}.constructor.prototype == Object.prototype while Object.create(null) doesn't inherit from anywhere and thus has no properties at all.

In other words: A javascript object inherits from Object by default, unless you explicitly create it specifying null as its prototype, as in Object.create(null).

{} would instead be equivalent to Object.create(Object.prototype).

In Chrome Devtool you can see that Object.create(null) have no __proto which {} have.

enter image description here

edited Aug 28 '17 at 11:13

TryingToImprove

3,74011732

answered Mar 20 '13 at 8:37

Peter Herdenborg

4,49011320

add a comment |

151

I think they are not equivalent. If I'm not mistaking, {}.constructor.prototype == Object.prototype while Object.create(null) doesn't inherit from anywhere and thus has no properties at all.

In other words: A javascript object inherits from Object by default, unless you explicitly create it specifying null as its prototype, as in Object.create(null).

{} would instead be equivalent to Object.create(Object.prototype).

In Chrome Devtool you can see that Object.create(null) have no __proto which {} have.

enter image description here

edited Aug 28 '17 at 11:13

TryingToImprove

3,74011732

answered Mar 20 '13 at 8:37

Peter Herdenborg

4,49011320

add a comment |

151

I think they are not equivalent. If I'm not mistaking, {}.constructor.prototype == Object.prototype while Object.create(null) doesn't inherit from anywhere and thus has no properties at all.

In other words: A javascript object inherits from Object by default, unless you explicitly create it specifying null as its prototype, as in Object.create(null).

{} would instead be equivalent to Object.create(Object.prototype).

In Chrome Devtool you can see that Object.create(null) have no __proto which {} have.

enter image description here

edited Aug 28 '17 at 11:13

TryingToImprove

3,74011732

answered Mar 20 '13 at 8:37

Peter Herdenborg

4,49011320

I think they are not equivalent. If I'm not mistaking, {}.constructor.prototype == Object.prototype while Object.create(null) doesn't inherit from anywhere and thus has no properties at all.

In other words: A javascript object inherits from Object by default, unless you explicitly create it specifying null as its prototype, as in Object.create(null).

{} would instead be equivalent to Object.create(Object.prototype).

In Chrome Devtool you can see that Object.create(null) have no __proto which {} have.

enter image description here

edited Aug 28 '17 at 11:13

TryingToImprove

3,74011732

answered Mar 20 '13 at 8:37

Peter Herdenborg

4,49011320

edited Aug 28 '17 at 11:13

TryingToImprove

3,74011732

edited Aug 28 '17 at 11:13

TryingToImprove

3,74011732

edited Aug 28 '17 at 11:13

TryingToImprove

3,74011732

answered Mar 20 '13 at 8:37

Peter Herdenborg

4,49011320

answered Mar 20 '13 at 8:37

Peter Herdenborg

4,49011320

answered Mar 20 '13 at 8:37

Peter Herdenborg

4,49011320

add a comment |

They are definitely not equivalent. I'm writing this answer to more fully explain why it makes a difference.

var p = {};

Creates an object that inherits the properties and methods from Object.

var p2 = Object.create(null);

Creates an object that doesn't inherit anything.

if (Object.prototype.hasOwnProperty.call(p, 'toString')) {

    // we actually inserted a 'toString' key into p

}

_{Note that it is fine to assign something to p.toString, it will simply override the inherited toString function on p.}

Note that you can't just do p.hasOwnProperty('toString') because you may have inserted a key "hasOwnProperty" into p, so we force it to use the implementation in Object.

On the other hand, if you use method 2 above, then you won't have to worry about things from Object appearing in the map.

You can't check for the existence of a property with a simple if like this:

// Unreliable:

if (p[someKey]) {

    // ...

}

answered Jan 12 '14 at 19:29

doug65536

5,05413045

3

A simpler alternative for checking for the existence of a property is: if (someKey in p) {

– mrcrowl
Nov 4 '16 at 7:51

2

@mrcrowl Only if they used Object.create(null). I prefer not to make assumptions like that, even if you were absolutely right that it used Object.create(null), the code could change, the object could be replaced with one that inherits Object at some point. hasOwnProperty always works.

– doug65536
Nov 4 '16 at 8:13

1

I feel being careful about something like this should be unnecessary. I appreciate your answer but documentation should give you the api necessary to work with whatever code you're working with. If you're grabbing some random code from github, then you can fork it and be safe from less documented updates. Not to mention {} is so much more prevalent than Object.create(null), that if your code accidentally grabs an inherited property at this point, you likely have way bigger bugs to worry about. I can only see people using Object.create(null) as a minor optimization.

– aaaaaa
Sep 13 '17 at 21:16

Double negation !!p[key] works good with Object.create(null). But hasKey = (key, input) => Object.prototype.hasOwnProperty.call(input, key) is not bad either

– andreid
May 2 '18 at 10:03

> Note that you can't just do p.hasOwnProperty('toString') because you may have inserted a key "hasOwnProperty" into p, so we force it to use the implementation in Object. That's is unnecessary. In this case, you can't use any methods in p because every method could be inserted and so become not safe.

– xianshenglu
Dec 6 '18 at 2:13

|
show 2 more comments

They are definitely not equivalent. I'm writing this answer to more fully explain why it makes a difference.

var p = {};

Creates an object that inherits the properties and methods from Object.

var p2 = Object.create(null);

Creates an object that doesn't inherit anything.

if (Object.prototype.hasOwnProperty.call(p, 'toString')) {

    // we actually inserted a 'toString' key into p

}

_{Note that it is fine to assign something to p.toString, it will simply override the inherited toString function on p.}

Note that you can't just do p.hasOwnProperty('toString') because you may have inserted a key "hasOwnProperty" into p, so we force it to use the implementation in Object.

On the other hand, if you use method 2 above, then you won't have to worry about things from Object appearing in the map.

You can't check for the existence of a property with a simple if like this:

// Unreliable:

if (p[someKey]) {

    // ...

}

answered Jan 12 '14 at 19:29

doug65536

5,05413045

3

A simpler alternative for checking for the existence of a property is: if (someKey in p) {

– mrcrowl
Nov 4 '16 at 7:51

2

@mrcrowl Only if they used Object.create(null). I prefer not to make assumptions like that, even if you were absolutely right that it used Object.create(null), the code could change, the object could be replaced with one that inherits Object at some point. hasOwnProperty always works.

– doug65536
Nov 4 '16 at 8:13

1

I feel being careful about something like this should be unnecessary. I appreciate your answer but documentation should give you the api necessary to work with whatever code you're working with. If you're grabbing some random code from github, then you can fork it and be safe from less documented updates. Not to mention {} is so much more prevalent than Object.create(null), that if your code accidentally grabs an inherited property at this point, you likely have way bigger bugs to worry about. I can only see people using Object.create(null) as a minor optimization.

– aaaaaa
Sep 13 '17 at 21:16

Double negation !!p[key] works good with Object.create(null). But hasKey = (key, input) => Object.prototype.hasOwnProperty.call(input, key) is not bad either

– andreid
May 2 '18 at 10:03

> Note that you can't just do p.hasOwnProperty('toString') because you may have inserted a key "hasOwnProperty" into p, so we force it to use the implementation in Object. That's is unnecessary. In this case, you can't use any methods in p because every method could be inserted and so become not safe.

– xianshenglu
Dec 6 '18 at 2:13

|
show 2 more comments

They are definitely not equivalent. I'm writing this answer to more fully explain why it makes a difference.

var p = {};

Creates an object that inherits the properties and methods from Object.

var p2 = Object.create(null);

Creates an object that doesn't inherit anything.

if (Object.prototype.hasOwnProperty.call(p, 'toString')) {

    // we actually inserted a 'toString' key into p

}

_{Note that it is fine to assign something to p.toString, it will simply override the inherited toString function on p.}

Note that you can't just do p.hasOwnProperty('toString') because you may have inserted a key "hasOwnProperty" into p, so we force it to use the implementation in Object.

On the other hand, if you use method 2 above, then you won't have to worry about things from Object appearing in the map.

You can't check for the existence of a property with a simple if like this:

// Unreliable:

if (p[someKey]) {

    // ...

}

answered Jan 12 '14 at 19:29

doug65536

5,05413045

They are definitely not equivalent. I'm writing this answer to more fully explain why it makes a difference.

var p = {};

Creates an object that inherits the properties and methods from Object.

var p2 = Object.create(null);

Creates an object that doesn't inherit anything.

if (Object.prototype.hasOwnProperty.call(p, 'toString')) {

    // we actually inserted a 'toString' key into p

}

_{Note that it is fine to assign something to p.toString, it will simply override the inherited toString function on p.}

Note that you can't just do p.hasOwnProperty('toString') because you may have inserted a key "hasOwnProperty" into p, so we force it to use the implementation in Object.

On the other hand, if you use method 2 above, then you won't have to worry about things from Object appearing in the map.

You can't check for the existence of a property with a simple if like this:

// Unreliable:

if (p[someKey]) {

    // ...

}

answered Jan 12 '14 at 19:29

doug65536

5,05413045

answered Jan 12 '14 at 19:29

doug65536

5,05413045

answered Jan 12 '14 at 19:29

doug65536

5,05413045

answered Jan 12 '14 at 19:29

doug65536

5,05413045

3

A simpler alternative for checking for the existence of a property is: if (someKey in p) {

– mrcrowl
Nov 4 '16 at 7:51

2

@mrcrowl Only if they used Object.create(null). I prefer not to make assumptions like that, even if you were absolutely right that it used Object.create(null), the code could change, the object could be replaced with one that inherits Object at some point. hasOwnProperty always works.

– doug65536
Nov 4 '16 at 8:13

1

I feel being careful about something like this should be unnecessary. I appreciate your answer but documentation should give you the api necessary to work with whatever code you're working with. If you're grabbing some random code from github, then you can fork it and be safe from less documented updates. Not to mention {} is so much more prevalent than Object.create(null), that if your code accidentally grabs an inherited property at this point, you likely have way bigger bugs to worry about. I can only see people using Object.create(null) as a minor optimization.

– aaaaaa
Sep 13 '17 at 21:16

Double negation !!p[key] works good with Object.create(null). But hasKey = (key, input) => Object.prototype.hasOwnProperty.call(input, key) is not bad either

– andreid
May 2 '18 at 10:03

> Note that you can't just do p.hasOwnProperty('toString') because you may have inserted a key "hasOwnProperty" into p, so we force it to use the implementation in Object. That's is unnecessary. In this case, you can't use any methods in p because every method could be inserted and so become not safe.

– xianshenglu
Dec 6 '18 at 2:13

|
show 2 more comments

3

A simpler alternative for checking for the existence of a property is: if (someKey in p) {

– mrcrowl
Nov 4 '16 at 7:51

2

@mrcrowl Only if they used Object.create(null). I prefer not to make assumptions like that, even if you were absolutely right that it used Object.create(null), the code could change, the object could be replaced with one that inherits Object at some point. hasOwnProperty always works.

– doug65536
Nov 4 '16 at 8:13

1

I feel being careful about something like this should be unnecessary. I appreciate your answer but documentation should give you the api necessary to work with whatever code you're working with. If you're grabbing some random code from github, then you can fork it and be safe from less documented updates. Not to mention {} is so much more prevalent than Object.create(null), that if your code accidentally grabs an inherited property at this point, you likely have way bigger bugs to worry about. I can only see people using Object.create(null) as a minor optimization.

– aaaaaa
Sep 13 '17 at 21:16

Double negation !!p[key] works good with Object.create(null). But hasKey = (key, input) => Object.prototype.hasOwnProperty.call(input, key) is not bad either

– andreid
May 2 '18 at 10:03

> Note that you can't just do p.hasOwnProperty('toString') because you may have inserted a key "hasOwnProperty" into p, so we force it to use the implementation in Object. That's is unnecessary. In this case, you can't use any methods in p because every method could be inserted and so become not safe.

– xianshenglu
Dec 6 '18 at 2:13

A simpler alternative for checking for the existence of a property is: if (someKey in p) {

– mrcrowl
Nov 4 '16 at 7:51

@mrcrowl Only if they used Object.create(null). I prefer not to make assumptions like that, even if you were absolutely right that it used Object.create(null), the code could change, the object could be replaced with one that inherits Object at some point. hasOwnProperty always works.

– doug65536
Nov 4 '16 at 8:13

I feel being careful about something like this should be unnecessary. I appreciate your answer but documentation should give you the api necessary to work with whatever code you're working with. If you're grabbing some random code from github, then you can fork it and be safe from less documented updates. Not to mention {} is so much more prevalent than Object.create(null), that if your code accidentally grabs an inherited property at this point, you likely have way bigger bugs to worry about. I can only see people using Object.create(null) as a minor optimization.

– aaaaaa
Sep 13 '17 at 21:16

Double negation !!p[key] works good with Object.create(null). But hasKey = (key, input) => Object.prototype.hasOwnProperty.call(input, key) is not bad either

– andreid
May 2 '18 at 10:03

> Note that you can't just do p.hasOwnProperty('toString') because you may have inserted a key "hasOwnProperty" into p, so we force it to use the implementation in Object. That's is unnecessary. In this case, you can't use any methods in p because every method could be inserted and so become not safe.

– xianshenglu
Dec 6 '18 at 2:13

|
show 2 more comments

If someone is looking for implementing Object.create(null), just to know how it works. It is written using proto which is non-standard and hence, I do not recommend it.

function objectCreateMimic()

{

  /*optional parameters: prototype_object, own_properties*/

  var P = arguments.length>0?arguments[0]:-1;

  var Q = arguments.length>1?arguments[1]:null;

  var o = {};

  if(P!==null && typeof P === "object")

  {

    o.__proto__ = P;

  }

  else if(P===null)

  {

    o.__proto__ = null;

  }

  if(Q!==null && typeof Q === "object")

  {

   for(var key in Q)

   {

     o[key] = Q[key];

   }

  }

  return o;

}

Note: I wrote this, out of curiosity, and it is only written in simple terms, for instance, I am not transferring the property descriptors from the second object to the return object.

edited Nov 19 '14 at 7:07

answered Nov 19 '14 at 6:51

Aravind

2,50011631

1

Note that as of ECMAScript's release in summer, __proto__ will now officially be part of the language.

– Chiru
Mar 20 '15 at 0:55

1

Why -1 in arguments.length>0?arguments[0]:-1;?

– happy_marmoset
Dec 3 '15 at 9:39

@happy_marmoset late response, but it looks like it's just a non-null placeholder so that the Object prototype is retained if the first argument isn't given. Variable names could be a lot better here.

– Mike Hill
Jul 31 '17 at 0:11

Also, the second parameter should describe the property descriptors rather than the actual properties themselves. See reference here: developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…

– Mike Hill
Jul 31 '17 at 0:16

add a comment |

If someone is looking for implementing Object.create(null), just to know how it works. It is written using proto which is non-standard and hence, I do not recommend it.

function objectCreateMimic()

{

  /*optional parameters: prototype_object, own_properties*/

  var P = arguments.length>0?arguments[0]:-1;

  var Q = arguments.length>1?arguments[1]:null;

  var o = {};

  if(P!==null && typeof P === "object")

  {

    o.__proto__ = P;

  }

  else if(P===null)

  {

    o.__proto__ = null;

  }

  if(Q!==null && typeof Q === "object")

  {

   for(var key in Q)

   {

     o[key] = Q[key];

   }

  }

  return o;

}

Note: I wrote this, out of curiosity, and it is only written in simple terms, for instance, I am not transferring the property descriptors from the second object to the return object.

edited Nov 19 '14 at 7:07

answered Nov 19 '14 at 6:51

Aravind

2,50011631

1

Note that as of ECMAScript's release in summer, __proto__ will now officially be part of the language.

– Chiru
Mar 20 '15 at 0:55

1

Why -1 in arguments.length>0?arguments[0]:-1;?

– happy_marmoset
Dec 3 '15 at 9:39

@happy_marmoset late response, but it looks like it's just a non-null placeholder so that the Object prototype is retained if the first argument isn't given. Variable names could be a lot better here.

– Mike Hill
Jul 31 '17 at 0:11

Also, the second parameter should describe the property descriptors rather than the actual properties themselves. See reference here: developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…

– Mike Hill
Jul 31 '17 at 0:16

add a comment |

If someone is looking for implementing Object.create(null), just to know how it works. It is written using proto which is non-standard and hence, I do not recommend it.

function objectCreateMimic()

{

  /*optional parameters: prototype_object, own_properties*/

  var P = arguments.length>0?arguments[0]:-1;

  var Q = arguments.length>1?arguments[1]:null;

  var o = {};

  if(P!==null && typeof P === "object")

  {

    o.__proto__ = P;

  }

  else if(P===null)

  {

    o.__proto__ = null;

  }

  if(Q!==null && typeof Q === "object")

  {

   for(var key in Q)

   {

     o[key] = Q[key];

   }

  }

  return o;

}

Note: I wrote this, out of curiosity, and it is only written in simple terms, for instance, I am not transferring the property descriptors from the second object to the return object.

edited Nov 19 '14 at 7:07

answered Nov 19 '14 at 6:51

Aravind

2,50011631

If someone is looking for implementing Object.create(null), just to know how it works. It is written using proto which is non-standard and hence, I do not recommend it.

function objectCreateMimic()

{

  /*optional parameters: prototype_object, own_properties*/

  var P = arguments.length>0?arguments[0]:-1;

  var Q = arguments.length>1?arguments[1]:null;

  var o = {};

  if(P!==null && typeof P === "object")

  {

    o.__proto__ = P;

  }

  else if(P===null)

  {

    o.__proto__ = null;

  }

  if(Q!==null && typeof Q === "object")

  {

   for(var key in Q)

   {

     o[key] = Q[key];

   }

  }

  return o;

}

Note: I wrote this, out of curiosity, and it is only written in simple terms, for instance, I am not transferring the property descriptors from the second object to the return object.

edited Nov 19 '14 at 7:07

answered Nov 19 '14 at 6:51

Aravind

2,50011631

edited Nov 19 '14 at 7:07

answered Nov 19 '14 at 6:51

Aravind

2,50011631

answered Nov 19 '14 at 6:51

Aravind

2,50011631

answered Nov 19 '14 at 6:51

Aravind

2,50011631

1

Note that as of ECMAScript's release in summer, __proto__ will now officially be part of the language.

– Chiru
Mar 20 '15 at 0:55

1

Why -1 in arguments.length>0?arguments[0]:-1;?

– happy_marmoset
Dec 3 '15 at 9:39

@happy_marmoset late response, but it looks like it's just a non-null placeholder so that the Object prototype is retained if the first argument isn't given. Variable names could be a lot better here.

– Mike Hill
Jul 31 '17 at 0:11

Also, the second parameter should describe the property descriptors rather than the actual properties themselves. See reference here: developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…

– Mike Hill
Jul 31 '17 at 0:16

add a comment |

1

Note that as of ECMAScript's release in summer, __proto__ will now officially be part of the language.

– Chiru
Mar 20 '15 at 0:55

1

Why -1 in arguments.length>0?arguments[0]:-1;?

– happy_marmoset
Dec 3 '15 at 9:39

@happy_marmoset late response, but it looks like it's just a non-null placeholder so that the Object prototype is retained if the first argument isn't given. Variable names could be a lot better here.

– Mike Hill
Jul 31 '17 at 0:11

Also, the second parameter should describe the property descriptors rather than the actual properties themselves. See reference here: developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…

– Mike Hill
Jul 31 '17 at 0:16

Note that as of ECMAScript's release in summer, __proto__ will now officially be part of the language.

– Chiru
Mar 20 '15 at 0:55

Why -1 in arguments.length>0?arguments[0]:-1;?

– happy_marmoset
Dec 3 '15 at 9:39

@happy_marmoset late response, but it looks like it's just a non-null placeholder so that the Object prototype is retained if the first argument isn't given. Variable names could be a lot better here.

– Mike Hill
Jul 31 '17 at 0:11

Also, the second parameter should describe the property descriptors rather than the actual properties themselves. See reference here: developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…

– Mike Hill
Jul 31 '17 at 0:16

add a comment |

answered Apr 12 '18 at 19:16

Praveen Kishor

6951716

add a comment |

answered Apr 12 '18 at 19:16

Praveen Kishor

6951716

add a comment |

answered Apr 12 '18 at 19:16

Praveen Kishor

6951716

answered Apr 12 '18 at 19:16

Praveen Kishor

6951716

answered Apr 12 '18 at 19:16

Praveen Kishor

6951716

answered Apr 12 '18 at 19:16

Praveen Kishor

6951716

answered Apr 12 '18 at 19:16

Praveen Kishor

6951716

add a comment |

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