Is there a null coalescing operator in JavaScript

Question

Is there a null coalescing operator in Javascript   For example  in C   I can do this   String someString   null  var whatIWant   someString     Cookies      The best approximation I can figure out for Javascript is using the conditional operator   var someString   null  var whatIWant   someString   someString    Cookies      Which is sorta icky IMHO  Can I do better

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Now it has full support in latest version of major browsers like Chrome  Edge  Firefox   Safari etc  Here s the comparison between the null operator and Nullish Coalescing Operator  const response             settings                nullValue  null              height  400              animationDuration  0              headerText                  showSplashScreen  false                         OR Operator        const undefinedValue   response settings undefinedValue     Default Value       Default Value      const nullValue   response settings nullValue     Default Value       Default Value      const headerText   response settings headerText     Hello  world         Hello  world       const animationDuration   response settings animationDuration    300      300     const showSplashScreen   response settings showSplashScreen    true      true        Nullish Coalescing Operator        const undefinedValue   response settings undefinedValue     Default Value       Default Value      const nullValue   response settings nullValue      Default Value       Default Value      const headerText   response settings headerText     Hello  world              const animationDuration   response settings animationDuration    300     0     const showSplashScreen   response settings showSplashScreen    true      false

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If    as a replacement of C  s    isn t good enough in your case  because it swallows empty strings and zeros  you can always write your own function    function  N value  ifnull        if  value     null    value     undefined        return ifnull      return value       var whatIWant    N someString   Cookies

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Update  JavaScript now supports the nullish coalescing operator       It returns its right-hand-side operand when its left-hand-side operand is null or undefined  and otherwise returns its left-hand-side operand    Please check compatibility before using it     The JavaScript equivalent of the C  null coalescing operator      is using a logical OR        var whatIWant   someString     Cookies      There are cases  clarified below  that the behaviour won t match that of C   but this is the general  terse way of assigning default alternative values in JavaScript     Clarification  Regardless of the type of the first operand  if casting it to a Boolean results in false  the assignment will use the second operand  Beware of all the cases below   alert Boolean null       false alert Boolean undefined       false alert Boolean 0       false alert Boolean          false alert Boolean  false        true -- gotcha       This means   var whatIWant   null    new ShinyObject       is a new shiny object var whatIWant   undefined     well defined      is  well defined  var whatIWant   0    42     is 42 var whatIWant          a million bucks      is  a million bucks  var whatIWant    false      no way      is  false

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After reading your clarification   Ates Goral s answer provides how to perform the same operation you re doing in C  in JavaScript    Gumbo s answer provides the best way to check for null  however  it s important to note the difference in    versus     in JavaScript especially when it comes to issues of checking for undefined and or null   There s a really good article about the difference in two terms here  Basically  understand that if you use    instead of      JavaScript will try to coalesce the values you re comparing and return what the result of the comparison after this coalescence

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After reading your clarification   Ates Goral s answer provides how to perform the same operation you re doing in C  in JavaScript    Gumbo s answer provides the best way to check for null  however  it s important to note the difference in    versus     in JavaScript especially when it comes to issues of checking for undefined and or null   There s a really good article about the difference in two terms here  Basically  understand that if you use    instead of      JavaScript will try to coalesce the values you re comparing and return what the result of the comparison after this coalescence

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It will hopefully be available soon in Javascript  as it is in proposal phase as of Apr  2020  You can monitor the status here for compatibility and support - https   developer mozilla org en-US docs Web JavaScript Reference Operators Nullish coalescing operator  For people using Typescript  you can use the nullish coalescing operator from Typescript 3 7  From the docs -      You can think of this feature - the    operator - as a way to    fall   back    to a default value when dealing with null or undefined  When we   write code like      let x   foo    bar         this is a new way to say that the value foo will be used when it   s    present     but when it   s null or undefined    calculate bar   in its place

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It will hopefully be available soon in Javascript  as it is in proposal phase as of Apr  2020  You can monitor the status here for compatibility and support - https   developer mozilla org en-US docs Web JavaScript Reference Operators Nullish coalescing operator  For people using Typescript  you can use the nullish coalescing operator from Typescript 3 7  From the docs -      You can think of this feature - the    operator - as a way to    fall   back    to a default value when dealing with null or undefined  When we   write code like      let x   foo    bar         this is a new way to say that the value foo will be used when it   s    present     but when it   s null or undefined    calculate bar   in its place

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Now it has full support in latest version of major browsers like Chrome  Edge  Firefox   Safari etc  Here s the comparison between the null operator and Nullish Coalescing Operator  const response             settings                nullValue  null              height  400              animationDuration  0              headerText                  showSplashScreen  false                         OR Operator        const undefinedValue   response settings undefinedValue     Default Value       Default Value      const nullValue   response settings nullValue     Default Value       Default Value      const headerText   response settings headerText     Hello  world         Hello  world       const animationDuration   response settings animationDuration    300      300     const showSplashScreen   response settings showSplashScreen    true      true        Nullish Coalescing Operator        const undefinedValue   response settings undefinedValue     Default Value       Default Value      const nullValue   response settings nullValue      Default Value       Default Value      const headerText   response settings headerText     Hello  world              const animationDuration   response settings animationDuration    300     0     const showSplashScreen   response settings showSplashScreen    true      false

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beware of the JavaScript specific definition of null  there are two definitions for  no value  in javascript  1  Null  when a variable is null  it means it contains no data in it  but the variable is already defined in the code  like this   var myEmptyValue   1  myEmptyValue   null  if   myEmptyValue     null     window alert  it is null         alerts   in such case  the type of your variable is actually Object  test it   window alert typeof myEmptyValue      prints Object    Undefined  when a variable has not been defined before in the code  and as expected  it does not contain any value  like this   if   myUndefinedValue     undefined     window alert  it is undefined         alerts    if such case  the type of your variable is  undefined    notice that if you use the type-converting comparison operator       JavaScript will act equally for both of these empty-values  to distinguish between them  always use the type-strict comparison operator

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Nobody has mentioned in here the potential for NaN  which--to me--is also a null-ish value  So  I thought I d add my two-cents   For the given code   var a      b   null      c   parseInt  Not a number        d   0      e           f   1     If you were to use the    operator  you get the first non-false value   var result   a    b    c    d    e    f     result     1   If you use the typical coalesce method  as posted here  you will get c  which has the value  NaN  var result   coalesce a b c d e f      result toString        NaN    Neither of these seem right to me   In my own little world of coalesce logic  which may differ from your world  I consider undefined  null  and NaN as all being  null-ish    So  I would expect to get back d  zero  from the coalesce method   If anyone s brain works like mine  and you want to exclude NaN  then this method will accomplish that   function coalesce         var i  undefined  arg       for  i 0  i  lt  arguments length  i               arg   arguments i           if  arg     null  amp  amp  arg     undefined              amp  amp   typeof arg      number     arg toString        NaN                   return arg                      return null      For those who want the code as short as possible  and don t mind a little lack of clarity  you can also use this as suggested by  impinball  This takes advantage of the fact that NaN is never equal to NaN   You can read up more on that here  Why is NaN not equal to NaN   function coalesce         var i  arg       for  i 0  i  lt  arguments length  i               arg   arguments i           if  arg    null  amp  amp  arg     arg       arg     arg is false for NaN             return arg                      return null

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Note that React s create-react-app tool-chain supports the null-coalescing since version 3 3 0  released 5 12 2019   From the release notes      Optional Chaining and Nullish Coalescing Operators      We now support the optional chaining and nullish coalescing operators      Optional chaining a         undefined if  a  is null undefined b  c     undefined if  b  is null undefined     Nullish coalescing undefined     some other default      result   some other default  null     some other default      result   some other default         some other default      result     0    300     result  0 false    true     result  false    This said  in case you use create-react-app 3 3 0  you can start using the null-coalesce operator already today in your React apps

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Nobody has mentioned in here the potential for NaN  which--to me--is also a null-ish value  So  I thought I d add my two-cents   For the given code   var a      b   null      c   parseInt  Not a number        d   0      e           f   1     If you were to use the    operator  you get the first non-false value   var result   a    b    c    d    e    f     result     1   If you use the typical coalesce method  as posted here  you will get c  which has the value  NaN  var result   coalesce a b c d e f      result toString        NaN    Neither of these seem right to me   In my own little world of coalesce logic  which may differ from your world  I consider undefined  null  and NaN as all being  null-ish    So  I would expect to get back d  zero  from the coalesce method   If anyone s brain works like mine  and you want to exclude NaN  then this method will accomplish that   function coalesce         var i  undefined  arg       for  i 0  i  lt  arguments length  i               arg   arguments i           if  arg     null  amp  amp  arg     undefined              amp  amp   typeof arg      number     arg toString        NaN                   return arg                      return null      For those who want the code as short as possible  and don t mind a little lack of clarity  you can also use this as suggested by  impinball  This takes advantage of the fact that NaN is never equal to NaN   You can read up more on that here  Why is NaN not equal to NaN   function coalesce         var i  arg       for  i 0  i  lt  arguments length  i               arg   arguments i           if  arg    null  amp  amp  arg     arg       arg     arg is false for NaN             return arg                      return null

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function coalesce         var len   arguments length      for  var i 0  i lt len  i              if  arguments i      null  amp  amp  arguments i      undefined                return arguments i                       return null     var xyz       xyz val   coalesce null  undefined  xyz val  5       xyz val now contains 5   this solution works like the SQL coalesce function  it accepts any number of arguments  and returns null if none of them have a value   It behaves like the C     operator in the sense that     false  and 0 are considered NOT NULL and therefore count as actual values   If you come from a  net background  this will be the most natural feeling solution

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Note that React s create-react-app tool-chain supports the null-coalescing since version 3 3 0  released 5 12 2019   From the release notes      Optional Chaining and Nullish Coalescing Operators      We now support the optional chaining and nullish coalescing operators      Optional chaining a         undefined if  a  is null undefined b  c     undefined if  b  is null undefined     Nullish coalescing undefined     some other default      result   some other default  null     some other default      result   some other default         some other default      result     0    300     result  0 false    true     result  false    This said  in case you use create-react-app 3 3 0  you can start using the null-coalesce operator already today in your React apps

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Yes  it is coming soon  See proposal here and implementation status here   It looks like this   x    y   Example  const response       settings        nullValue  null      height  400      animationDuration  0      headerText          showSplashScreen  false         const undefinedValue   response settings  undefinedValue     some other default      result   some other default  const nullValue   response settings  nullValue     some other default      result   some other default  const headerText   response settings  headerText     Hello  world       result     const animationDuration   response settings  animationDuration    300     result  0 const showSplashScreen   response settings  showSplashScreen    true     result  false

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Yes  and its proposal is Stage 4 now  This means that the proposal is ready for inclusion in the formal ECMAScript standard  You can already use it in recent desktop versions of Chrome  Edge and Firefox  but we will have to wait for a bit longer until this feature reaches cross-browser stability   Have a look at the following example to demonstrate its behavior    x000D   x000D     note  this will work only if you re running latest versions of aforementioned browsers x000D  const var1   undefined  x000D  const var2    fallback value   x000D   x000D  const result   var1    var2  x000D  console log  Nullish coalescing results in    result     x000D   x000D   x000D    Previous example is equivalent to    x000D   x000D  const var1   undefined  x000D  const var2    fallback value   x000D   x000D  const result    var1     null  amp  amp  var1     undefined    x000D      var1   x000D      var2  x000D  console log  Nullish coalescing results in    result     x000D   x000D   x000D    Note that nullish coalescing will not threat falsy values the way the    operator did  it only checks for undefined or null values   hence the following snippet will act as follows    x000D   x000D     note  this will work only if you re running latest versions of aforementioned browsers x000D  const var1          empty string x000D  const var2    fallback value   x000D   x000D  const result   var1    var2  x000D  console log  Nullish coalescing results in    result     x000D   x000D   x000D      For TypesScript users  starting off TypeScript 3 7  this feature is also available now

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Logical nullish assignment  2020  solution A new operator is currently being added to the browsers       This combines the null coalescing operator    with the assignment operator     NOTE  This is not common in public browser versions yet  Will update as availability changes       checks if the variable is undefined or null  short-circuiting if already defined  If not  the right-side value is assigned to the variable  Basic Examples let a             undefined let b   null let c   false  a     true     true b     true     true c     true     false  Object Array Examples let x     quot foo quot   let y     foo   quot fizz quot     x 0       quot bar quot       quot foo quot  x 1       quot bar quot       quot bar quot   y foo      quot buzz quot       quot fizz quot  y bar      quot buzz quot       quot buzz quot   x     Array    quot foo quot    quot bar quot    y     Object   foo   quot fizz quot   bar   quot buzz quot     Browser Support Sept 2020 - 3 7  Mozilla Documentation

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After reading your clarification   Ates Goral s answer provides how to perform the same operation you re doing in C  in JavaScript    Gumbo s answer provides the best way to check for null  however  it s important to note the difference in    versus     in JavaScript especially when it comes to issues of checking for undefined and or null   There s a really good article about the difference in two terms here  Basically  understand that if you use    instead of      JavaScript will try to coalesce the values you re comparing and return what the result of the comparison after this coalescence

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function coalesce         var len   arguments length      for  var i 0  i lt len  i              if  arguments i      null  amp  amp  arguments i      undefined                return arguments i                       return null     var xyz       xyz val   coalesce null  undefined  xyz val  5       xyz val now contains 5   this solution works like the SQL coalesce function  it accepts any number of arguments  and returns null if none of them have a value   It behaves like the C     operator in the sense that     false  and 0 are considered NOT NULL and therefore count as actual values   If you come from a  net background  this will be the most natural feeling solution

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beware of the JavaScript specific definition of null  there are two definitions for  no value  in javascript  1  Null  when a variable is null  it means it contains no data in it  but the variable is already defined in the code  like this   var myEmptyValue   1  myEmptyValue   null  if   myEmptyValue     null     window alert  it is null         alerts   in such case  the type of your variable is actually Object  test it   window alert typeof myEmptyValue      prints Object    Undefined  when a variable has not been defined before in the code  and as expected  it does not contain any value  like this   if   myUndefinedValue     undefined     window alert  it is undefined         alerts    if such case  the type of your variable is  undefined    notice that if you use the type-converting comparison operator       JavaScript will act equally for both of these empty-values  to distinguish between them  always use the type-strict comparison operator

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Need to support old browser and have a object hierarchy body head eyes 0     body  head  eyes  may be null   may use this     body       head       eyes      0     left eye

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Logical nullish assignment  2020  solution A new operator is currently being added to the browsers       This combines the null coalescing operator    with the assignment operator     NOTE  This is not common in public browser versions yet  Will update as availability changes       checks if the variable is undefined or null  short-circuiting if already defined  If not  the right-side value is assigned to the variable  Basic Examples let a             undefined let b   null let c   false  a     true     true b     true     true c     true     false  Object Array Examples let x     quot foo quot   let y     foo   quot fizz quot     x 0       quot bar quot       quot foo quot  x 1       quot bar quot       quot bar quot   y foo      quot buzz quot       quot fizz quot  y bar      quot buzz quot       quot buzz quot   x     Array    quot foo quot    quot bar quot    y     Object   foo   quot fizz quot   bar   quot buzz quot     Browser Support Sept 2020 - 3 7  Mozilla Documentation

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Yes  and its proposal is Stage 4 now  This means that the proposal is ready for inclusion in the formal ECMAScript standard  You can already use it in recent desktop versions of Chrome  Edge and Firefox  but we will have to wait for a bit longer until this feature reaches cross-browser stability   Have a look at the following example to demonstrate its behavior    x000D   x000D     note  this will work only if you re running latest versions of aforementioned browsers x000D  const var1   undefined  x000D  const var2    fallback value   x000D   x000D  const result   var1    var2  x000D  console log  Nullish coalescing results in    result     x000D   x000D   x000D    Previous example is equivalent to    x000D   x000D  const var1   undefined  x000D  const var2    fallback value   x000D   x000D  const result    var1     null  amp  amp  var1     undefined    x000D      var1   x000D      var2  x000D  console log  Nullish coalescing results in    result     x000D   x000D   x000D    Note that nullish coalescing will not threat falsy values the way the    operator did  it only checks for undefined or null values   hence the following snippet will act as follows    x000D   x000D     note  this will work only if you re running latest versions of aforementioned browsers x000D  const var1          empty string x000D  const var2    fallback value   x000D   x000D  const result   var1    var2  x000D  console log  Nullish coalescing results in    result     x000D   x000D   x000D      For TypesScript users  starting off TypeScript 3 7  this feature is also available now

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beware of the JavaScript specific definition of null  there are two definitions for  no value  in javascript  1  Null  when a variable is null  it means it contains no data in it  but the variable is already defined in the code  like this   var myEmptyValue   1  myEmptyValue   null  if   myEmptyValue     null     window alert  it is null         alerts   in such case  the type of your variable is actually Object  test it   window alert typeof myEmptyValue      prints Object    Undefined  when a variable has not been defined before in the code  and as expected  it does not contain any value  like this   if   myUndefinedValue     undefined     window alert  it is undefined         alerts    if such case  the type of your variable is  undefined    notice that if you use the type-converting comparison operator       JavaScript will act equally for both of these empty-values  to distinguish between them  always use the type-strict comparison operator

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Update  JavaScript now supports the nullish coalescing operator       It returns its right-hand-side operand when its left-hand-side operand is null or undefined  and otherwise returns its left-hand-side operand    Please check compatibility before using it     The JavaScript equivalent of the C  null coalescing operator      is using a logical OR        var whatIWant   someString     Cookies      There are cases  clarified below  that the behaviour won t match that of C   but this is the general  terse way of assigning default alternative values in JavaScript     Clarification  Regardless of the type of the first operand  if casting it to a Boolean results in false  the assignment will use the second operand  Beware of all the cases below   alert Boolean null       false alert Boolean undefined       false alert Boolean 0       false alert Boolean          false alert Boolean  false        true -- gotcha       This means   var whatIWant   null    new ShinyObject       is a new shiny object var whatIWant   undefined     well defined      is  well defined  var whatIWant   0    42     is 42 var whatIWant          a million bucks      is  a million bucks  var whatIWant    false      no way      is  false

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Yes  it is coming soon  See proposal here and implementation status here   It looks like this   x    y   Example  const response       settings        nullValue  null      height  400      animationDuration  0      headerText          showSplashScreen  false         const undefinedValue   response settings  undefinedValue     some other default      result   some other default  const nullValue   response settings  nullValue     some other default      result   some other default  const headerText   response settings  headerText     Hello  world       result     const animationDuration   response settings  animationDuration    300     result  0 const showSplashScreen   response settings  showSplashScreen    true     result  false

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beware of the JavaScript specific definition of null  there are two definitions for  no value  in javascript  1  Null  when a variable is null  it means it contains no data in it  but the variable is already defined in the code  like this   var myEmptyValue   1  myEmptyValue   null  if   myEmptyValue     null     window alert  it is null         alerts   in such case  the type of your variable is actually Object  test it   window alert typeof myEmptyValue      prints Object    Undefined  when a variable has not been defined before in the code  and as expected  it does not contain any value  like this   if   myUndefinedValue     undefined     window alert  it is undefined         alerts    if such case  the type of your variable is  undefined    notice that if you use the type-converting comparison operator       JavaScript will act equally for both of these empty-values  to distinguish between them  always use the type-strict comparison operator

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If    as a replacement of C  s    isn t good enough in your case  because it swallows empty strings and zeros  you can always write your own function    function  N value  ifnull        if  value     null    value     undefined        return ifnull      return value       var whatIWant    N someString   Cookies

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Need to support old browser and have a object hierarchy body head eyes 0     body  head  eyes  may be null   may use this     body       head       eyes      0     left eye

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Too much talk  there are two items here   Logical OR  const foo          default string   console log foo      output is  default string   Nullish coalescing operator  const foo          default string   console log foo      output is empty string i e     The nullish coalescing operator      is a logical operator that returns its right-hand side operand when its left-hand side operand is null or undefined  and otherwise returns its left-hand side operand  https   developer mozilla org en-US docs Web JavaScript Reference Operators Nullish coalescing operator

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If    as a replacement of C  s    isn t good enough in your case  because it swallows empty strings and zeros  you can always write your own function    function  N value  ifnull        if  value     null    value     undefined        return ifnull      return value       var whatIWant    N someString   Cookies

User · Answer

Update  JavaScript now supports the nullish coalescing operator       It returns its right-hand-side operand when its left-hand-side operand is null or undefined  and otherwise returns its left-hand-side operand    Please check compatibility before using it     The JavaScript equivalent of the C  null coalescing operator      is using a logical OR        var whatIWant   someString     Cookies      There are cases  clarified below  that the behaviour won t match that of C   but this is the general  terse way of assigning default alternative values in JavaScript     Clarification  Regardless of the type of the first operand  if casting it to a Boolean results in false  the assignment will use the second operand  Beware of all the cases below   alert Boolean null       false alert Boolean undefined       false alert Boolean 0       false alert Boolean          false alert Boolean  false        true -- gotcha       This means   var whatIWant   null    new ShinyObject       is a new shiny object var whatIWant   undefined     well defined      is  well defined  var whatIWant   0    42     is 42 var whatIWant          a million bucks      is  a million bucks  var whatIWant    false      no way      is  false

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Too much talk  there are two items here   Logical OR  const foo          default string   console log foo      output is  default string   Nullish coalescing operator  const foo          default string   console log foo      output is empty string i e     The nullish coalescing operator      is a logical operator that returns its right-hand side operand when its left-hand side operand is null or undefined  and otherwise returns its left-hand side operand  https   developer mozilla org en-US docs Web JavaScript Reference Operators Nullish coalescing operator

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Update  JavaScript now supports the nullish coalescing operator       It returns its right-hand-side operand when its left-hand-side operand is null or undefined  and otherwise returns its left-hand-side operand    Please check compatibility before using it     The JavaScript equivalent of the C  null coalescing operator      is using a logical OR        var whatIWant   someString     Cookies      There are cases  clarified below  that the behaviour won t match that of C   but this is the general  terse way of assigning default alternative values in JavaScript     Clarification  Regardless of the type of the first operand  if casting it to a Boolean results in false  the assignment will use the second operand  Beware of all the cases below   alert Boolean null       false alert Boolean undefined       false alert Boolean 0       false alert Boolean          false alert Boolean  false        true -- gotcha       This means   var whatIWant   null    new ShinyObject       is a new shiny object var whatIWant   undefined     well defined      is  well defined  var whatIWant   0    42     is 42 var whatIWant          a million bucks      is  a million bucks  var whatIWant    false      no way      is  false

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Ok a proper answer  Does it exist in JavaScript  Yes  it does  BUT  It s currently as of 2020-02-06 at Stage 3 and is not supported everywhere  yet  Follow the link in URL below and go to the  Specifications  and  Browser compatibility  headers for more info on where it is at   Quote from  https   developer mozilla org en-US docs Web JavaScript Reference Operators Nullish coalescing operator     The nullish coalescing operator      is a logical operator that   returns its right-hand side operand when its left-hand side operand is   null or undefined  and otherwise returns its left-hand side operand       Contrary to the logical OR      operator  the left operand is returned   if it is a falsy value which is not null or undefined  In other words    if you use    to provide some default value to another variable foo    you may encounter unexpected behaviors if you consider some falsy   values as usable  eg     or 0   See below for more examples    Want examples  Follow the link I posted  it has everything

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After reading your clarification   Ates Goral s answer provides how to perform the same operation you re doing in C  in JavaScript    Gumbo s answer provides the best way to check for null  however  it s important to note the difference in    versus     in JavaScript especially when it comes to issues of checking for undefined and or null   There s a really good article about the difference in two terms here  Basically  understand that if you use    instead of      JavaScript will try to coalesce the values you re comparing and return what the result of the comparison after this coalescence

User · Answer

If    as a replacement of C  s    isn t good enough in your case  because it swallows empty strings and zeros  you can always write your own function    function  N value  ifnull        if  value     null    value     undefined        return ifnull      return value       var whatIWant    N someString   Cookies

User · Answer

Ok a proper answer  Does it exist in JavaScript  Yes  it does  BUT  It s currently as of 2020-02-06 at Stage 3 and is not supported everywhere  yet  Follow the link in URL below and go to the  Specifications  and  Browser compatibility  headers for more info on where it is at   Quote from  https   developer mozilla org en-US docs Web JavaScript Reference Operators Nullish coalescing operator     The nullish coalescing operator      is a logical operator that   returns its right-hand side operand when its left-hand side operand is   null or undefined  and otherwise returns its left-hand side operand       Contrary to the logical OR      operator  the left operand is returned   if it is a falsy value which is not null or undefined  In other words    if you use    to provide some default value to another variable foo    you may encounter unexpected behaviors if you consider some falsy   values as usable  eg     or 0   See below for more examples    Want examples  Follow the link I posted  it has everything

[javascript] Is there a "null coalescing" operator in JavaScript?

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