Create an empty object in JavaScript with or new Object

Question

There are two different ways to create an empty object in JavaScript   var objectA      var objectB   new Object     Is there any difference in how the script engine handles them  Is there any reason to use one over the other   Similarly it is also possible to create an empty array using different syntax   var arrayA      var arrayB   new Array

User · Accepted Answer

Objects  There is no benefit to using new Object    - whereas     can make your code more compact  and more readable   For defining empty objects they re technically the same   The    syntax is shorter  neater  less Java-ish   and allows you to instantly populate the object inline - like so   var myObject             title    Frog           url       img picture jpg           width   300          height  200            Arrays  For arrays  there s similarly almost no benefit to ever using new Array    over     - with one minor exception   var emptyArray   new Array 100     creates a 100 item long array with all slots containing undefined - which may be  nice useful in certain situations  such as  new Array 9   join  Na-Na       Batman      My recommendation   Never use new Object    - it s clunkier than     and looks silly  Always use     - except when you need to quickly create an  empty  array with a predefined length

User · Answer

Yes  There is a difference  they re not the same  It s true that you ll get the same results but the engine works in a different way for both of them  One of them is an object literal  and the other one is a constructor  two different ways of creating an object in javascript   var objectA        This is an object literal  var objectB   new Object     This is the object constructor   In JS everything is an object  but you should be aware about the following thing with new Object    It can receive a parameter  and depending on that parameter  it will create a string  a number  or just an empty object   For example  new Object 1   will return a Number  new Object  hello   will return a string  it means that the object constructor can delegate -depending on the parameter- the object creation to other constructors like string  number  etc    It s highly important to keep this in mind when you re managing dynamic data to create objects    Many authors recommend not to use the object constructor when you can use a certain literal notation instead  where you will be sure that what you re creating is what you re expecting to have in your code   I suggest you to do a further reading on the differences between literal notation and constructors on javascript to find more details

User · Answer

Array instantiation performance  If you wish to create an array with no length   var arr       is faster than var arr   new Array     If you wish to create an empty array with a certain length   var arr   new Array x   is faster than var arr       arr x-1    undefined   For benchmarks click the following  https   jsfiddle net basickarl ktbbry5b   I do not however know the memory footprint of both  I can imagine that new Array   takes up more space

User · Answer

I believe    was recommended in one of the Javascript vids on here as a good coding convention  new is necessary for pseudoclassical inheritance  the var obj       way helps to remind you that this is not a classical object oriented language but a prototypal one  Thus the only time you would really need new is when you are using constructors functions  For example   var Mammal   function  name      this name   name      Mammal prototype get name   function        return this name     Mammal prototype says   function       return this saying            Then it is used like so   var aMammal   new Mammal  Me warm-blooded    var name   aMammal get name      Another advantage to using    as oppose to new Object is you can use it to do JSON-style object literals

User · Answer

The object and array literal syntax       was introduced in JavaScript 1 2  so is not available  and will produce a syntax error  in versions of Netscape Navigator prior to 4 0   My fingers still default to saying new Array    but I am a very old man  Thankfully Netscape 3 is not a browser many people ever have to consider today

User · Answer

I believe    was recommended in one of the Javascript vids on here as a good coding convention  new is necessary for pseudoclassical inheritance  the var obj       way helps to remind you that this is not a classical object oriented language but a prototypal one  Thus the only time you would really need new is when you are using constructors functions  For example   var Mammal   function  name      this name   name      Mammal prototype get name   function        return this name     Mammal prototype says   function       return this saying            Then it is used like so   var aMammal   new Mammal  Me warm-blooded    var name   aMammal get name      Another advantage to using    as oppose to new Object is you can use it to do JSON-style object literals

User · Answer

These have the same end result  but I would simply add that using the literal syntax can help one become accustomed to the syntax of JSON  a string-ified subset of JavaScript literal object syntax   so it might be a good practice to get into    One other thing  you might have subtle errors if you forget to use the new operator  So  using literals will help you avoid that problem   Ultimately  it will depend on the situation as well as preference

User · Answer

This is essentially the same thing  Use whatever you find more convenient

User · Answer

I believe    was recommended in one of the Javascript vids on here as a good coding convention  new is necessary for pseudoclassical inheritance  the var obj       way helps to remind you that this is not a classical object oriented language but a prototypal one  Thus the only time you would really need new is when you are using constructors functions  For example   var Mammal   function  name      this name   name      Mammal prototype get name   function        return this name     Mammal prototype says   function       return this saying            Then it is used like so   var aMammal   new Mammal  Me warm-blooded    var name   aMammal get name      Another advantage to using    as oppose to new Object is you can use it to do JSON-style object literals

User · Answer

var objectA        is a lot quicker and  in my experience  more commonly used  so it s probably best to adopt the  standard  and save some typing

User · Answer

var objectA        is a lot quicker and  in my experience  more commonly used  so it s probably best to adopt the  standard  and save some typing

User · Answer

OK  there are just 2 different ways to do the same thing  One called object literal and the other one is a function constructor   But read on  there are couple of things I d like to share   Using    makes your code more readable  while creating instances of Object or other built-in functions not recommended     Also  Object function gets parameters as it s a function  like Object params     but    is pure way to start an object in JavaScript     Using object literal makes your code looks much cleaner and easier to read for other developers and it s inline with best practices in JavaScript     While Object in Javascript can be almost anything     only points to javascript objects  for the test how it works  do below in your javascript code or console   var n   new Object 1     Number    PrimitiveValue    1    Surprisingly  it s creating a Number   var a   new Object  1 2 3       1  2  3    And this is creating a Array   var s   new Object  alireza      String  0   a   1   l   2   i   3   r   4   e   5   z   6   a   length  7    PrimitiveValue     alireza     and this weird result for String   So if you are creating an object  it s recommended to use object literal  to have a standard code and avoid any code accident like above  also performance wise using    is better in my experience

User · Answer

var objectA        is a lot quicker and  in my experience  more commonly used  so it s probably best to adopt the  standard  and save some typing

User · Answer

I believe    was recommended in one of the Javascript vids on here as a good coding convention  new is necessary for pseudoclassical inheritance  the var obj       way helps to remind you that this is not a classical object oriented language but a prototypal one  Thus the only time you would really need new is when you are using constructors functions  For example   var Mammal   function  name      this name   name      Mammal prototype get name   function        return this name     Mammal prototype says   function       return this saying            Then it is used like so   var aMammal   new Mammal  Me warm-blooded    var name   aMammal get name      Another advantage to using    as oppose to new Object is you can use it to do JSON-style object literals

User · Answer

This is essentially the same thing  Use whatever you find more convenient

User · Answer

var objectA        is a lot quicker and  in my experience  more commonly used  so it s probably best to adopt the  standard  and save some typing

User · Answer

Var Obj        This is the most used and simplest method  Using var Obj   new Obj     is not preferred  There is no need to use new Object    For simplicity  readability and execution speed  use the first one  the object literal method

User · Answer

Array instantiation performance  If you wish to create an array with no length   var arr       is faster than var arr   new Array     If you wish to create an empty array with a certain length   var arr   new Array x   is faster than var arr       arr x-1    undefined   For benchmarks click the following  https   jsfiddle net basickarl ktbbry5b   I do not however know the memory footprint of both  I can imagine that new Array   takes up more space

User · Answer

This is essentially the same thing  Use whatever you find more convenient

User · Answer

Yes  There is a difference  they re not the same  It s true that you ll get the same results but the engine works in a different way for both of them  One of them is an object literal  and the other one is a constructor  two different ways of creating an object in javascript   var objectA        This is an object literal  var objectB   new Object     This is the object constructor   In JS everything is an object  but you should be aware about the following thing with new Object    It can receive a parameter  and depending on that parameter  it will create a string  a number  or just an empty object   For example  new Object 1   will return a Number  new Object  hello   will return a string  it means that the object constructor can delegate -depending on the parameter- the object creation to other constructors like string  number  etc    It s highly important to keep this in mind when you re managing dynamic data to create objects    Many authors recommend not to use the object constructor when you can use a certain literal notation instead  where you will be sure that what you re creating is what you re expecting to have in your code   I suggest you to do a further reading on the differences between literal notation and constructors on javascript to find more details

User · Answer

This is essentially the same thing  Use whatever you find more convenient

User · Answer

The object and array literal syntax       was introduced in JavaScript 1 2  so is not available  and will produce a syntax error  in versions of Netscape Navigator prior to 4 0   My fingers still default to saying new Array    but I am a very old man  Thankfully Netscape 3 is not a browser many people ever have to consider today

User · Answer

These have the same end result  but I would simply add that using the literal syntax can help one become accustomed to the syntax of JSON  a string-ified subset of JavaScript literal object syntax   so it might be a good practice to get into    One other thing  you might have subtle errors if you forget to use the new operator  So  using literals will help you avoid that problem   Ultimately  it will depend on the situation as well as preference

User · Answer

The object and array literal syntax       was introduced in JavaScript 1 2  so is not available  and will produce a syntax error  in versions of Netscape Navigator prior to 4 0   My fingers still default to saying new Array    but I am a very old man  Thankfully Netscape 3 is not a browser many people ever have to consider today

User · Answer

Var Obj        This is the most used and simplest method  Using var Obj   new Obj     is not preferred  There is no need to use new Object    For simplicity  readability and execution speed  use the first one  the object literal method

User · Answer

These have the same end result  but I would simply add that using the literal syntax can help one become accustomed to the syntax of JSON  a string-ified subset of JavaScript literal object syntax   so it might be a good practice to get into    One other thing  you might have subtle errors if you forget to use the new operator  So  using literals will help you avoid that problem   Ultimately  it will depend on the situation as well as preference

User · Answer

The object and array literal syntax       was introduced in JavaScript 1 2  so is not available  and will produce a syntax error  in versions of Netscape Navigator prior to 4 0   My fingers still default to saying new Array    but I am a very old man  Thankfully Netscape 3 is not a browser many people ever have to consider today

User · Answer

OK  there are just 2 different ways to do the same thing  One called object literal and the other one is a function constructor   But read on  there are couple of things I d like to share   Using    makes your code more readable  while creating instances of Object or other built-in functions not recommended     Also  Object function gets parameters as it s a function  like Object params     but    is pure way to start an object in JavaScript     Using object literal makes your code looks much cleaner and easier to read for other developers and it s inline with best practices in JavaScript     While Object in Javascript can be almost anything     only points to javascript objects  for the test how it works  do below in your javascript code or console   var n   new Object 1     Number    PrimitiveValue    1    Surprisingly  it s creating a Number   var a   new Object  1 2 3       1  2  3    And this is creating a Array   var s   new Object  alireza      String  0   a   1   l   2   i   3   r   4   e   5   z   6   a   length  7    PrimitiveValue     alireza     and this weird result for String   So if you are creating an object  it s recommended to use object literal  to have a standard code and avoid any code accident like above  also performance wise using    is better in my experience

User · Answer

These have the same end result  but I would simply add that using the literal syntax can help one become accustomed to the syntax of JSON  a string-ified subset of JavaScript literal object syntax   so it might be a good practice to get into    One other thing  you might have subtle errors if you forget to use the new operator  So  using literals will help you avoid that problem   Ultimately  it will depend on the situation as well as preference

[javascript] Create an empty object in JavaScript with {} or new Object()?

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