Is it possible to sort a ES6 map object

Question

Is it possible to sort the entries of a es6 map object   var map   new Map    map set  2-1   foo   map set  0-1   bar     results in   map entries         0    2-1   foo        1    0-1   bar       Is it possible to sort the entries based on their keys   map entries         0    0-1   bar        1    2-1   foo

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As far as I see it s currently not possible to sort a Map properly   The other solutions where the Map is converted into an array and sorted this way have the following bug   var a   new Map   1  2    3 4    console log a         a   Map 2    1   gt  2  3   gt  4   var b   a  console log b         b   Map 2    1   gt  2  3   gt  4   a   new Map           this is when the sorting happens console log a  b      a   Map 0          b   Map 2    1   gt  2  3   gt  4    The sorting creates a new object and all other pointers to the unsorted object get broken

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Perhaps a more realistic example about not sorting a Map object but preparing the sorting up front before doing the Map  The syntax gets actually pretty compact if you do it like this  You can apply the sorting before the map function like this  with a sort function before map  Example from a React app I am working on using JSX syntax    Mark that I here define a sorting function inside using an arrow function that returns -1 if it is smaller and 0 otherwise sorted on a property of the Javascript objects in the array I get from an API   report ProcedureCodes sort  a  b    gt  a NumericalOrder  lt  b NumericalOrder   -1   0  map  item  i    gt                           lt TableRow key  i  gt                                lt TableCell gt  item Code  lt  TableCell gt                               lt TableCell gt  item Text  lt  TableCell gt                                   lt TableCell gt  item NumericalOrder  lt  TableCell gt                               lt  TableRow gt

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The idea is to extract the keys of your map into an array  Sort this array  Then iterate over this sorted array  get its value pair from the unsorted map and put them into a new map  The new map will be in sorted order  The code below is it s implementation   var unsortedMap   new Map    unsortedMap set  2-1    foo    unsortedMap set  0-1    bar        Initialize your keys array var keys          Initialize your sorted maps object var sortedMap   new Map        Put keys in Array unsortedMap forEach function callback value  key  map        keys push key           Sort keys array and go through them to put in and put them in sorted map keys sort   map function key        sortedMap set key  unsortedMap get key            View your sorted map console log sortedMap

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One way is to get the entries array  sort it  and then create a new Map with the sorted array   let ar       myMap entries     sortedArray   ar sort    sortedMap   new Map sortedArray     But if you don t want to create a new object  but to work on the same one  you can do something like this      Get an array of the keys and sort them let keys       myMap keys     sortedKeys   keys sort     sortedKeys forEach  key   gt        Delete the element and set it again at the end   const value   this get key     this delete key     this set key value

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You can convert to an array and call array soring methods on it       map  sort    etc

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The snippet below sorts given map by its keys and maps the keys to key-value objects again  I used localeCompare function since my map was string- string object map   var hash     x    xx    t    tt    y    yy    Object keys hash  sort  a  b    gt  a localeCompare b   map function  i                var o                   o i    hash i               return o                result    t  tt     x  xx     y   yy

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Short answer  new Map     map  sort  a  b    gt         Some sort function comparing keys with a 0  b 0  or values with a 1  b 1       If you re expecting strings  As normal for  sort you need to return -1 if lower and 0 if equal  for strings  the recommended way is using  localeCompare   which does this correctly and automatically handles awkward characters like    where the position varies by user locale  So here s how to sort a map by string keys   new Map     map  sort  a  b    gt  String a 0   localeCompare b 0         and by string values   new Map     map  sort  a  b    gt  String a 1   localeCompare b 1       In detail with examples tldr     map entries   is redundant  just    map is fine  and a lazy  sort   without passing a sort function risks weird edge case bugs caused by string coercion  The  entries   in     map entries     suggested in many answers  is redundant  probably adding an extra iteration of the map unless the JS engine optimises that away for you  In the simple test case  you can do what the question asks for with  new Map     map  sort        which  if the keys are all strings  compares squashed and coerced comma-joined key-value strings like  2-1 foo  and  0-1  object Object    returning a new Map with the new insertion order  Note  if you see only    in SO s console output  look in your real browser console  x000D   x000D  const map   new Map       2-1    foo        0-1     bar   bar          3-5        gt   fuz        3-2      baz         console log new Map     map  sort     x000D   x000D   x000D   HOWEVER  it s not a good practice to rely on coercion and stringification like this  You can get surprises like   x000D   x000D  const map   new Map       2    3 buh         2 1    foo        0 1     bar   bar          3 5        gt   fuz        3 2      baz             Compares  2 3 buh   with  2 1 foo     Therefore sorts   2    3 buh          AFTER         2 1    foo   console log  Buh    new Map     map  sort         Let s see exactly what each iteration is using as its comparator for  const iteration of map      console log iteration toString      x000D   x000D   x000D   Bugs like this are really hard to debug - don t risk it  If you want to sort on keys or values  it s best to access them explicitly with a 0  and b 0  in the sort function  like this  Note that we should return -1 and 1 for before and after  not false or 0 as with raw a 0   gt  b 0  because that is treated as equals   x000D   x000D  const map   new Map       2 1    this is overwritten        2 1    0 1        0 1    2 1        2 2    3 5        3 5    2 1        2     9 9       const sortStringKeys    a  b    gt  String a 0   localeCompare b 0   const sortStringValues    a  b    gt  String a 1   localeCompare b 1    console log  By keys    new Map     map  sort sortStringKeys    console log  By values    new Map     map  sort sortStringValues    x000D   x000D   x000D

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2 hours spent to get into details   Note that the answer for question is already given at https   stackoverflow com a 31159284 984471  However  the question has keys that are not usual ones  A clear  amp  general example with explanation  is below that provides some more clarity    Some more examples here  https   javascript info map-set You can copy-paste the below code to following link  and modify it for your specific use case  https   www jdoodle com execute-nodejs-online       let m1   new Map     m1 set 6 1      key 6 is number and type is preserved  can be strings too  m1 set 10 1   m1 set 100 1   m1 set 1 1   console log m1        string  sorted  even if keys are numbers  - default behaviour let m2   new Map      m1  sort                 is destructuring into individual elements         then    will catch elements in an array         then sort   sorts the array         since Map can take array as parameter to its constructor  a new Map is created console log  m2   m2       number sorted let m3   new Map     m1  sort  a  b    gt      if  a 0   gt  b 0   return 1    if  a 0     b 0   return 0    if  a 0   lt  b 0   return -1       console log  m3   m3       Output       Map   6   gt  1  10   gt  1  100   gt  1  1   gt  1      m2 Map   1   gt  1  10   gt  1  100   gt  1  6   gt  1                Note   1 10 100 6  sorted as strings  default               Note   if the keys were string the sort behavior will be same as this    m3 Map   1   gt  1  6   gt  1  10   gt  1  100   gt  1                Note   1 6 10 100  sorted as number  looks correct for number keys   Hope that helps

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Unfortunately  not really implemented in ES6  You have this feature with OrderedMap sort   from ImmutableJS or   sortBy   from Lodash

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Slight variation - I didn t have spread syntax and I wanted to work on an object instead of a Map  Object fromEntries Object entries apis  sort

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According MDN documentation   A Map object iterates its elements in insertion order   You could do it this way   x000D   x000D  var map   new Map    map set  2-1    foo    map set  0-1    bar    map set  3-1    baz     var mapAsc   new Map     map entries    sort      console log mapAsc  x000D   x000D   x000D   Using  sort    remember that the array is sorted according to each character s Unicode code point value  according to the string conversion of each element  So 2-1  0-1  3-1 will be sorted correctly

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Convert Map to an array using Array from  sort array  convert back to Map  e g   new Map    Array      from eventsByDate       sort  a  b    gt             a 0   b 0  is the key of the map       return a 0  - b 0

[javascript] Is it possible to sort a ES6 map object?

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