Does Typescript support the operator And what s it called

Question

Does Typescript currently  or are there plans to  support the safe navigation operator of     ie   var thing   foo  bar    same as  var thing    foo    foo bar   null    Also  is there a more common name for this operator  it s incedibly hard to google for

User · Answer

We created this util method while working on Phonetradr which can give you type-safe access to deep properties with Typescript:

_x000D_

/**_x000D_
 * Type-safe access of deep property of an object_x000D_
 *_x000D_
 * @param obj                   Object to get deep property_x000D_
 * @param unsafeDataOperation   Function that returns the deep property_x000D_
 * @param valueIfFail           Value to return in case if there is no such property_x000D_
 */_x000D_
export function getInSafe<O,T>(obj: O, unsafeDataOperation: (x: O) => T, valueIfFail?: any) : T {_x000D_
    try {_x000D_
        return unsafeDataOperation(obj)_x000D_
    } catch (error) {_x000D_
        return valueIfFail;_x000D_
    }_x000D_
}_x000D_
_x000D_
//Example usage:_x000D_
getInSafe(sellTicket, x => x.phoneDetails.imeiNumber, '');_x000D_
_x000D_
//Example from above_x000D_
getInSafe(foo, x => x.bar.check, null);

_x000D_

User · Answer

Update  Yes its supported now   It just got released with TypeScript 3 7   https   devblogs microsoft com typescript announcing-typescript-3-7   It is called optional chaining   https   devblogs microsoft com typescript announcing-typescript-3-7  optional-chaining  With it the following   let x   foo  bar baz       is equivalent to    let x    foo     null    foo     undefined        undefined       foo bar baz      Old answer  There is an open feature request for this on github where you can voice your opinion   desire   https   github com Microsoft TypeScript issues 16

User · Answer

This is defined in the ECMAScript Optional Chaining specification  so we should probably refer to optional chaining when we discuss this  Likely implementation   const result   a  b  c    The long and short of this one is that the TypeScript team are waiting for the ECMAScript specification to get tightened up  so their implementation can be non-breaking in the future  If they implemented something now  it would end up needing major changes if ECMAScript redefine their specification   See Optional Chaining Specification  Where something is never going to be standard JavaScript  the TypeScript team can implement as they see fit  but for future ECMAScript additions  they want to preserve semantics even if they give early access  as they have for so many other features   Short Cuts  So all of JavaScripts funky operators are available  including the type conversions such as     var n  number    myString     convert to number var b  bool     myString     convert to bool   Manual Solution  But back to the question  I have an obtuse example of how you can do a similar thing in JavaScript  and therefore TypeScript  although I m definitely not suggesting it is a graceful as the feature you are really after    foo      bar    So if foo is undefined the result is undefined and if foo is defined and has a property named bar that has a value  the result is that value   I put an example on JSFiddle   This looks quite sketchy for longer examples   var postCode     person      address      postcode    Chain Function  If you are desperate for a shorter version while the specification is still up in the air  I use this method in some cases  It evaluates the expression and returns a default if the chain can t be satisfied or ends up null undefined  note the    is important here  we don t want to use     as we want a bit of positive juggling here    function chain lt T gt  exp       gt  T  d  T        try           let val   exp            if  val    null                return val                  catch         return d     let obj1    a     b   string            a            b   c                c  console log chain      gt  obj1 a b   Nothing      obj1         a             Nothing  console log chain      gt  obj1 a b   Nothing      obj1            Nothing  console log chain      gt  obj1 a b   Nothing      obj1   null       Nothing  console log chain      gt  obj1 a b   Nothing

User · Answer

I don t generally recommend this approach  watch out for performance concerns   but you can use the spread operator to shallow clone an object  which you can then access the property on     const person     personId  123  firstName   Simon      const firstName        person   firstName    This works because the type of  firstName  is  propagated  through   I ll use this most frequently when I have a find      expression that can return null and I need a single property from it       this would cause an error  this ID doesn t exist   const people    person    const firstName2   people find p   gt  p personId    999  firstName       this works - but copies every property over so raises performance concerns  const firstName3        people find p   gt  p personId    999    firstName    There may be some edge cases with the way typescript infers types and this won t compile  but this should generally work

User · Answer

It s called optional chaining and It s in Typescript  3 7     Optional chaining lets us write code where we can immediately stop   running some expressions if we run into a null or undefined

User · Answer

Edit Nov  13  2019   As of November 5  2019 TypeScript 3 7 has shipped and it now supports    the optional chaining operator      https   www typescriptlang org docs handbook release-notes typescript-3-7 html optional-chaining    For Historical Purposes Only   Edit  I have updated the answer thanks to fracz comment    TypeScript 2 0 released    It s not the same as    Safe Navigator in C    See this answer for more details   https   stackoverflow com a 38875179 1057052  This will only tell the compiler that the value is not null or undefined  This will not check if the value is null or undefined    TypeScript Non-null assertion operator     Compiled with --strictNullChecks function validateEntity e   Entity           Throw exception if e is null or invalid entity    function processEntity e   Entity        validateEntity e       let s   e  name      Assert that e is non-null and access name

User · Answer

As answered before  it s currently still being considered but it has been dead in the water for a few years by now   Building on the existing answers  here s the most concise manual version I can think of   jsfiddle  function val lt T gt  valueSupplier       gt  T   T     try   return valueSupplier      catch  err    return undefined       let obj1    a     b   string        a    b   c       console log val      gt  obj1 a b        c   obj1     a        console log val      gt  obj1 a b       undefined console log val      gt  obj1 a b      Nothing        Nothing   obj1       console log val      gt  obj1 a b      Nothing        Nothing   obj1   null  console log val      gt  obj1 a b      Nothing        Nothing    It simply silently fails on missing property errors  It falls back to the standard syntax for determining default value  which can be omitted completely as well     Although this works for simple cases  if you need more complex stuff such as calling a function and then access a property on the result  then any other errors are swallowed as well  Bad design   In the above case  an optimized version of the other answer posted here is the better option   jsfiddle  function o lt T gt  obj   T  def  T      as T   T       return obj    def     let obj1    a     b   string        a    b   c       console log o o o obj1  a   b       c   obj1     a        console log o o o obj1  a   b      undefined console log o o o obj1  a   b     Nothing        Nothing   obj1       console log o o o obj1  a   b     Nothing        Nothing   obj1   null  console log o o o obj1  a   b     Nothing        Nothing    A more complex example   o foo        map  n    gt  n id      You can also go the other way and use something like Lodash    get    It is concise  but the compiler won t be able to judge the validity of the properties used   console log   get obj1   a b c

User · Answer

Update  it is supported as of TypeScript 3 7 and called Optional chaining  https   www typescriptlang org docs handbook release-notes typescript-3-7 html optional-chaining  I can t find any reference to it whatsoever in the TypeScript language specification   As far as what to call this operator in CoffeeScript  it s called the existential operator  specifically  the  accessor variant  of the existential operator    From CoffeeScript s documentation on Operators      The accessor variant of the existential operator    can be used to soak up null references in a chain of properties  Use it instead of the dot accessor   in cases where the base value may be null or undefined    So  the accessor variant of the existential operator appears to be the proper way to refer to this operator  and TypeScript does not currently appear to support it  although others have expressed a desire for this functionality

User · Answer

It s finally here   Here are a few examples      properties foo  bar foo  bar   foo  bar baz   foo  bar  baz       indexing foo   0  foo    bar       check if a function is defined before invoking foo     foo bar     foo  bar       But it doesn t work exactly the same as your assumption   Instead of evaluating  foo  bar   to this little code snippet we are all used to writing  foo   foo bar   null   it actually evaluates to   foo     null    foo     undefined        undefined       foo bar   which works for all the falsey values like an empty string  0 or false   I just don t have an explanation as to why they don t compile it to foo    null

User · Answer

Not as nice as a single    but it works   var thing   foo  amp  amp  foo bar    null    You can use as many  amp  amp  as you like   var thing   foo  amp  amp  foo bar  amp  amp  foo bar check  amp  amp  foo bar check x    null

User · Answer

Operator    is not supported in TypeScript version 2 0   So I use the following function   export function o lt T gt  someObject  T  defaultValue  T      as T    T       if  typeof someObject      undefined     someObject     null          return defaultValue      else         return someObject      the usage looks like this   o o o test  prop1  prop2   plus  you can set a default value   o o o o test  prop1  prop2   none     It works really well with IntelliSense in Visual Studio

User · Answer

Not yet  as of September  2019   but since the  safe navigation operator  is now at Stage 3  it s being implemented in TypeScript   Watch this issue for updates   https   github com microsoft TypeScript issues 16  Several engines have early implementations   JSC  https   bugs webkit org show bug cgi id 200199  V8  https   bugs chromium org p v8 issues detail id 9553  SM  https   bugzilla mozilla org show bug cgi id 1566143   via https   github com tc39 proposal-optional-chaining issues 115 issue-475422578   You can install a plugin to support it now   npm install --save-dev ts-optchain   In your tsconfig json      tsconfig json        compilerOptions              plugins                    transform    ts-optchain transform                          I expect this answer to be out of date in the next 6 months or so  but hopefully it will help someone in the meantime

User · Answer

get obj   address street name   works great for JavaScript where you have no types  But for TypeScript we need the real Elvis operator

User · Answer

The Elvis      Optional Chaining Operator is supported in TypeScript 3 7   You can use it to check for null values  cats  miows returns null if cats is null or undefined   You can also use it for optional method calling  cats doMiow   5  will call doMiow if it exists   Property access is also possible  cats    miows     Reference  https   devblogs microsoft com typescript announcing-typescript-3-7-beta

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