Iterating over Typescript Map

Question

I m trying to iterate over a typescript map but I keep getting errors and I could not find any solution yet for such a trivial problem   My code is   myMap   Map lt string  boolean gt   for let key of myMap keys         console log key       And I get the Error      Type  IterableIteratorShim lt  string  boolean    is not an array type or a string type    Full Stack Trace    Error  Typescript found the following errors     home project tmp broccoli type script compiler-input base path-q4GtzHgb tmp 0 src app project project-data service ts  21  20   Type  IterableIteratorShim lt  string  boolean  gt   is not an array type or a string type      at BroccoliTypeScriptCompiler  doIncrementalBuild   home project node modules angular-cli lib broccoli broccoli-typescript js 115 19      at BroccoliTypeScriptCompiler build   home project node modules angular-cli lib broccoli broccoli-typescript js 43 10      at  home project node modules broccoli-caching-writer index js 152 21     at lib rsvp  internal  tryCatch   home project node modules rsvp dist rsvp js 1036 16      at lib rsvp  internal  invokeCallback   home project node modules rsvp dist rsvp js 1048 17      at lib rsvp  internal  publish   home project node modules rsvp dist rsvp js 1019 11      at lib rsvp asap  flush   home project node modules rsvp dist rsvp js 1198 9      at  combinedTickCallback  internal process next tick js 67 7      at process  tickCallback  internal process next tick js 98 9    I m using angular-cli beta5 and typescript 1 8 10 and my target is es5  Has anyone had this Problem

User · Answer

I m using latest TS and node  v2 6 and v8 9 respectively  and I can do   let myMap   new Map lt string  boolean gt     myMap set  a   true   for  let  k  v  of myMap        console log k         v

User · Answer

If you don t really like nested functions  you can also iterate over the keys   myMap   Map lt string  boolean gt   for let key of myMap       if  myMap hasOwnProperty key            console log JSON stringify  key  key  value  myMap key               Note  you have to filter out the non-key iterations with the hasOwnProperty  if you don t do this  you get a warning or an error

User · Answer

Just a simple explanation to use it in an HTML document   If you have a Map of types  key  array  then you initialise the array this way   public cityShop  Map lt string  Shop   gt    new Map      And to iterate over it  you create an array from key values   Just use it as an array as in   keys   Array from this cityShop keys       Then  in HTML  you can use     ngFor  let key of keys    Inside this loop  you just get the array value with   this cityShop get key    Done

User · Answer

Just use Array from   method to convert it to an Array  myMap   Map lt string  boolean gt   for let key of Array from  myMap keys           console log key

User · Answer

Using Array from  Array prototype forEach    and arrow functions   Iterate over the keys   Array from myMap keys    forEach key   gt  console log key      Iterate over the values   Array from myMap values    forEach value   gt  console log value      Iterate over the entries   Array from myMap entries    forEach entry   gt  console log  Key      entry 0      Value      entry 1

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On Typescript 3 5 and Angular 8 LTS  it was required to cast the type as follows   for  let  k  v  of Object entries someMap         console log k  v

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es6  for  let  key  value  of map        console log key  value       es5  for  let entry of Array from map entries           let key   entry 0       let value   entry 1

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This worked for me  TypeScript Version  2 8 3  for  const  key  value  of Object entries myMap          console log key  value

User · Answer

You could use Map prototype forEach  value  key  map    gt  void  thisArg     void instead  Use it like this   myMap forEach  value  boolean  key  string    gt        console log key  value

User · Answer

This worked for me   Object keys myMap  map  key   gt        console log  key      key       console log  value      myMap key

User · Answer

You can also apply the array map method to the Map entries   iterable       myMap entries    map         key  value    string  number     gt  console log key  value       Also  as noted in other answers  you may have to enable down level iteration in your tsconfig json  under compiler options       downlevelIteration   true

User · Answer

Per the TypeScript 2 3 release notes on  New --downlevelIteration       for  of statements  Array Destructuring  and Spread elements in Array  Call  and New expressions support Symbol iterator in ES5 E3 if available when using --downlevelIteration   This is not enabled by default  Add  downlevelIteration   true to your tsconfig json  or pass --downlevelIteration flag to tsc  to get full iterator support   With this in place  you can write for  let keyval of myMap        and keyval s type will be automatically inferred     Why is this turned off by default  According to TypeScript contributor  aluanhaddad      It is optional because it has a very significant impact on the size of generated code  and potentially on performance  for all uses of iterables  including arrays     If you can target ES2015   target    es2015  in tsconfig json or tsc --target ES2015  or later  enabling downlevelIteration is a no-brainer  but if you re targeting ES5 ES3  you might benchmark to ensure iterator support doesn t impact performance  if it does  you might be better off with Array from conversion or forEach or some other workaround

[typescript] Iterating over Typescript Map

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