What is the obj?.prop syntax in javascript?












7















I was looking through a code and I came across this:



{{abc?.xvy=== tyu?abc?.xz:abc?.xz}}


I am unable to understand meaning of this expression. I know that it is Null-safe property access but I am bit confused about the chaining.
Any help is much appreciated






javascript ecmascript-5







share|improve this question

























  • Possible duplicate of Null-safe property access (and conditional assignment) in ES6/2015

    – adiga
    55 mins ago
















7















I was looking through a code and I came across this:



{{abc?.xvy=== tyu?abc?.xz:abc?.xz}}


I am unable to understand meaning of this expression. I know that it is Null-safe property access but I am bit confused about the chaining.
Any help is much appreciated






javascript ecmascript-5







share|improve this question

























  • Possible duplicate of Null-safe property access (and conditional assignment) in ES6/2015

    – adiga
    55 mins ago














7












7








7


0






I was looking through a code and I came across this:



{{abc?.xvy=== tyu?abc?.xz:abc?.xz}}


I am unable to understand meaning of this expression. I know that it is Null-safe property access but I am bit confused about the chaining.
Any help is much appreciated






javascript ecmascript-5







share|improve this question
















I was looking through a code and I came across this:



{{abc?.xvy=== tyu?abc?.xz:abc?.xz}}


I am unable to understand meaning of this expression. I know that it is Null-safe property access but I am bit confused about the chaining.
Any help is much appreciated






javascript ecmascript-5




javascript ecmascript-5






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited 16 mins ago







Apurva Pathak

















asked 1 hour ago









Apurva PathakApurva Pathak

1069




1069













  • Possible duplicate of Null-safe property access (and conditional assignment) in ES6/2015

    – adiga
    55 mins ago



















  • Possible duplicate of Null-safe property access (and conditional assignment) in ES6/2015

    – adiga
    55 mins ago

















Possible duplicate of Null-safe property access (and conditional assignment) in ES6/2015

– adiga
55 mins ago





Possible duplicate of Null-safe property access (and conditional assignment) in ES6/2015

– adiga
55 mins ago












4 Answers
4






active

oldest

votes


















3














Its new ES proposal called "optionals" for safe check reading for object properties. Above expression is equivalent to:



(abc && abc.xvy) === (tyu) ? (abc && abc.xz) : (abc && abc.xz)


You can find more details here: https://github.com/davidyaha/ecmascript-optionals-proposal






share|improve this answer





















  • 2





    OP's code doesn't have any standalone reference to an xz variable, though.

    – CertainPerformance
    13 mins ago



















5














This looks to be an example of the optional chaining proposal, which is still very much a work in progress (only at Stage 1). It's not actually implemented in vanilla JS environments yet. Using



obj?.prop


means: if obj is undefined or null, the expression evaluates to undefined. But otherwise, it will evaluate to the prop property on the object. This is syntax sugar for



obj && obj.prop


(using just obj.prop alone will throw if obj is undefined or null)



So, your



abc?.xvy=== tyu?abc?.xz:abc?.xz


will evaluate to true if the nested value abc?.xvy is equal to the nested value abc?.xz - or, it will evaluate to true if at least one of the nested values doesn't exist, and the other is undefined.



Spaced out for easier reading:



abc?.xvy === tyu

? abc?.xz

: abc?.xz


As you can see, both ? and : expressions are the same, making the conditional operator unnecessary here. An equivalent test (assuming that referencing tyu doesn't throw) would be



abc?.xvy === abc?.xz





share|improve this answer































    3














    It's called Null Propagation Operator.



    We can think of each ?. operator as a short circuit where "if the expression up until this point is null or undefined, then the whole expression evaluates to undefined".
    We could also optionally call functions.






    share|improve this answer































      -1














      It is called the elvis operator



      It is a part of the ECMAScript proposals to make code more readable and reduce the long && chains



      essentially, it creates a short-circuit check for null or undefined and prevents the "Cannot read property of undefined" errors. If the value exists, the latter part is evaluated.



      You can read more here : Is there a null-coalescing (Elvis) operator or safe navigation operator in javascript?






      share|improve this answer

























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        4 Answers
        4






        active

        oldest

        votes








        4 Answers
        4






        active

        oldest

        votes









        active

        oldest

        votes






        active

        oldest

        votes









        3














        Its new ES proposal called "optionals" for safe check reading for object properties. Above expression is equivalent to:



        (abc && abc.xvy) === (tyu) ? (abc && abc.xz) : (abc && abc.xz)


        You can find more details here: https://github.com/davidyaha/ecmascript-optionals-proposal






        share|improve this answer





















        • 2





          OP's code doesn't have any standalone reference to an xz variable, though.

          – CertainPerformance
          13 mins ago
















        3














        Its new ES proposal called "optionals" for safe check reading for object properties. Above expression is equivalent to:



        (abc && abc.xvy) === (tyu) ? (abc && abc.xz) : (abc && abc.xz)


        You can find more details here: https://github.com/davidyaha/ecmascript-optionals-proposal






        share|improve this answer





















        • 2





          OP's code doesn't have any standalone reference to an xz variable, though.

          – CertainPerformance
          13 mins ago














        3












        3








        3







        Its new ES proposal called "optionals" for safe check reading for object properties. Above expression is equivalent to:



        (abc && abc.xvy) === (tyu) ? (abc && abc.xz) : (abc && abc.xz)


        You can find more details here: https://github.com/davidyaha/ecmascript-optionals-proposal






        share|improve this answer















        Its new ES proposal called "optionals" for safe check reading for object properties. Above expression is equivalent to:



        (abc && abc.xvy) === (tyu) ? (abc && abc.xz) : (abc && abc.xz)


        You can find more details here: https://github.com/davidyaha/ecmascript-optionals-proposal







        share|improve this answer














        share|improve this answer



        share|improve this answer








        edited 11 mins ago

























        answered 58 mins ago









        Vishal RajoleVishal Rajole

        819815




        819815








        • 2





          OP's code doesn't have any standalone reference to an xz variable, though.

          – CertainPerformance
          13 mins ago














        • 2





          OP's code doesn't have any standalone reference to an xz variable, though.

          – CertainPerformance
          13 mins ago








        2




        2





        OP's code doesn't have any standalone reference to an xz variable, though.

        – CertainPerformance
        13 mins ago





        OP's code doesn't have any standalone reference to an xz variable, though.

        – CertainPerformance
        13 mins ago













        5














        This looks to be an example of the optional chaining proposal, which is still very much a work in progress (only at Stage 1). It's not actually implemented in vanilla JS environments yet. Using



        obj?.prop


        means: if obj is undefined or null, the expression evaluates to undefined. But otherwise, it will evaluate to the prop property on the object. This is syntax sugar for



        obj && obj.prop


        (using just obj.prop alone will throw if obj is undefined or null)



        So, your



        abc?.xvy=== tyu?abc?.xz:abc?.xz


        will evaluate to true if the nested value abc?.xvy is equal to the nested value abc?.xz - or, it will evaluate to true if at least one of the nested values doesn't exist, and the other is undefined.



        Spaced out for easier reading:



        abc?.xvy === tyu
        
? abc?.xz
        
: abc?.xz


        As you can see, both ? and : expressions are the same, making the conditional operator unnecessary here. An equivalent test (assuming that referencing tyu doesn't throw) would be



        abc?.xvy === abc?.xz





        share|improve this answer




























          5














          This looks to be an example of the optional chaining proposal, which is still very much a work in progress (only at Stage 1). It's not actually implemented in vanilla JS environments yet. Using



          obj?.prop


          means: if obj is undefined or null, the expression evaluates to undefined. But otherwise, it will evaluate to the prop property on the object. This is syntax sugar for



          obj && obj.prop


          (using just obj.prop alone will throw if obj is undefined or null)



          So, your



          abc?.xvy=== tyu?abc?.xz:abc?.xz


          will evaluate to true if the nested value abc?.xvy is equal to the nested value abc?.xz - or, it will evaluate to true if at least one of the nested values doesn't exist, and the other is undefined.



          Spaced out for easier reading:



          abc?.xvy === tyu
          
? abc?.xz
          
: abc?.xz


          As you can see, both ? and : expressions are the same, making the conditional operator unnecessary here. An equivalent test (assuming that referencing tyu doesn't throw) would be



          abc?.xvy === abc?.xz





          share|improve this answer


























            5












            5








            5







            This looks to be an example of the optional chaining proposal, which is still very much a work in progress (only at Stage 1). It's not actually implemented in vanilla JS environments yet. Using



            obj?.prop


            means: if obj is undefined or null, the expression evaluates to undefined. But otherwise, it will evaluate to the prop property on the object. This is syntax sugar for



            obj && obj.prop


            (using just obj.prop alone will throw if obj is undefined or null)



            So, your



            abc?.xvy=== tyu?abc?.xz:abc?.xz


            will evaluate to true if the nested value abc?.xvy is equal to the nested value abc?.xz - or, it will evaluate to true if at least one of the nested values doesn't exist, and the other is undefined.



            Spaced out for easier reading:



            abc?.xvy === tyu
            
? abc?.xz
            
: abc?.xz


            As you can see, both ? and : expressions are the same, making the conditional operator unnecessary here. An equivalent test (assuming that referencing tyu doesn't throw) would be



            abc?.xvy === abc?.xz





            share|improve this answer













            This looks to be an example of the optional chaining proposal, which is still very much a work in progress (only at Stage 1). It's not actually implemented in vanilla JS environments yet. Using



            obj?.prop


            means: if obj is undefined or null, the expression evaluates to undefined. But otherwise, it will evaluate to the prop property on the object. This is syntax sugar for



            obj && obj.prop


            (using just obj.prop alone will throw if obj is undefined or null)



            So, your



            abc?.xvy=== tyu?abc?.xz:abc?.xz


            will evaluate to true if the nested value abc?.xvy is equal to the nested value abc?.xz - or, it will evaluate to true if at least one of the nested values doesn't exist, and the other is undefined.



            Spaced out for easier reading:



            abc?.xvy === tyu
            
? abc?.xz
            
: abc?.xz


            As you can see, both ? and : expressions are the same, making the conditional operator unnecessary here. An equivalent test (assuming that referencing tyu doesn't throw) would be



            abc?.xvy === abc?.xz






            share|improve this answer












            share|improve this answer



            share|improve this answer










            answered 55 mins ago









            CertainPerformanceCertainPerformance

            84.3k154169




            84.3k154169























                3














                It's called Null Propagation Operator.



                We can think of each ?. operator as a short circuit where "if the expression up until this point is null or undefined, then the whole expression evaluates to undefined".
                We could also optionally call functions.






                share|improve this answer




























                  3














                  It's called Null Propagation Operator.



                  We can think of each ?. operator as a short circuit where "if the expression up until this point is null or undefined, then the whole expression evaluates to undefined".
                  We could also optionally call functions.






                  share|improve this answer


























                    3












                    3








                    3







                    It's called Null Propagation Operator.



                    We can think of each ?. operator as a short circuit where "if the expression up until this point is null or undefined, then the whole expression evaluates to undefined".
                    We could also optionally call functions.






                    share|improve this answer













                    It's called Null Propagation Operator.



                    We can think of each ?. operator as a short circuit where "if the expression up until this point is null or undefined, then the whole expression evaluates to undefined".
                    We could also optionally call functions.







                    share|improve this answer












                    share|improve this answer



                    share|improve this answer










                    answered 57 mins ago









                    Alex ParkAlex Park

                    412




                    412























                        -1














                        It is called the elvis operator



                        It is a part of the ECMAScript proposals to make code more readable and reduce the long && chains



                        essentially, it creates a short-circuit check for null or undefined and prevents the "Cannot read property of undefined" errors. If the value exists, the latter part is evaluated.



                        You can read more here : Is there a null-coalescing (Elvis) operator or safe navigation operator in javascript?






                        share|improve this answer






























                          -1














                          It is called the elvis operator



                          It is a part of the ECMAScript proposals to make code more readable and reduce the long && chains



                          essentially, it creates a short-circuit check for null or undefined and prevents the "Cannot read property of undefined" errors. If the value exists, the latter part is evaluated.



                          You can read more here : Is there a null-coalescing (Elvis) operator or safe navigation operator in javascript?






                          share|improve this answer




























                            -1












                            -1








                            -1







                            It is called the elvis operator



                            It is a part of the ECMAScript proposals to make code more readable and reduce the long && chains



                            essentially, it creates a short-circuit check for null or undefined and prevents the "Cannot read property of undefined" errors. If the value exists, the latter part is evaluated.



                            You can read more here : Is there a null-coalescing (Elvis) operator or safe navigation operator in javascript?






                            share|improve this answer















                            It is called the elvis operator



                            It is a part of the ECMAScript proposals to make code more readable and reduce the long && chains



                            essentially, it creates a short-circuit check for null or undefined and prevents the "Cannot read property of undefined" errors. If the value exists, the latter part is evaluated.



                            You can read more here : Is there a null-coalescing (Elvis) operator or safe navigation operator in javascript?







                            share|improve this answer














                            share|improve this answer



                            share|improve this answer








                            edited 29 mins ago

























                            answered 43 mins ago









                            Dhananjai PaiDhananjai Pai

                            828113




                            828113






























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