For loop in multidimensional javascript array

Question

Since now  I m using this loop to iterate over the elements of an array  which works fine even if I put objects with various properties inside of it   var cubes     for  i in cubes        cubes i  dimension      cubes i  position x      ecc       Now  let s suppose cubes   is declared this way  var cubes        Can I do this in Javascript  How can I then automatically iterate in  cubes 0  0  cubes 0  1  cubes 0  2  cubes 1  0  cubes 1  1  cubes 1  2  cubes 2  0  ecc      As a workaround  I can just declare   var cubes    var cubes1      and work separately with the two arrays  Is this a better solution

User · Answer

var cubes      string    string      string    string      for var i   0  i  lt  cubes length  i          for var j   0  j  lt  cubes i  length  j              console log cubes i  j

User · Answer

A bit too late  but this solution is nice and neat  const arr     1 2 3   4 5 6   7 8 9 10   for  let i of arr      for  let j of i        console log j    Should log numbers from 1 to 10         Or in your case   const arr     1 2 3   4 5 6   7 8 9   for  let  d1  d2  d3  of arr      console log    d1     d2     d3      Should return numbers from 1 to 9     Note  for     of loop is standardised in ES6  so only use this if you have an ES5 Javascript Complier  such as Babel   Another note  There are alternatives  but they have some subtle differences and behaviours  such as forEach    for   in  for   of and traditional for    It depends on your case to decide which one to use   ES6 also has  map     filter     find     reduce

User · Answer

If you re using ES2015 and you want to define your own object that iterates like a 2-D array  you can implement the iterator protocol by    Defining an   iterator function called Symbol iterator which returns       an object with a next   function that returns       an object with one or two properties  an optional value with the next value  if there is one  and a boolean done which is true if we re done iterating    A one-dimensional array iterator function would look like this        our custom Cubes object which implements the iterable protocol function Cubes         this cubes    1  2  3  4       this numVals   this cubes length          assign a function to the property Symbol iterator        which is a special property that the spread operator        and for  of construct both search for     this Symbol iterator    function         can t take args          var index   -1     keep an internal count of our index         var self   this     access vars methods in object scope             the   iterator method must return an object            with a  next    property  which will be called            implicitly to get the next value         return                  next   must return an object with a  done                   and optionally also a  value   property             next  function                     index                       if there s still some values  return next one                 if  index  lt  self numVals                        return                           value  self cubes index                           done  false                                                             else there s no more values left  so we re done                    IF YOU FORGET THIS YOU WILL LOOP FOREVER                  return  done  true                                      Now  we can treat our Cubes object like an iterable     var cube   new Cubes       construct our cube object     both call Symbol iterator function implicitly  console log     cube       spread operator for  var value of cube       for  of construct     console log value       To create our own 2-D iterable  instead of returning a value in our next   function  we can return another iterable     function Cubes         this cubes              1  2  3  4            5  6  7  8            9  10  11  12              this numRows   this cubes length      this numCols   this cubes 0  length     assumes all rows have same length      this Symbol iterator    function              var row   -1          var self   this              create a closure that returns an iterator            on the captured row index         function createColIterator currentRow                var col   -1              var colIterator                     column iterator implements iterable protocol             colIterator Symbol iterator    function                     return  next  function                         col                        if  col  lt  self numCols                               return raw value                         return                               value  self cubes currentRow  col                               done  false                                                                      return  done  true                                                 return colIterator                     return  next  function                 row                if  row  lt  self numRows                       instead of a value  return another iterator                 return                       value  createColIterator row                       done  false                                              return  done  true                         Now  we can use nested iteration     var cube   new Cubes        spread operator returns list of iterators      each of which can be spread to get values var rows       cube   console log     rows 0     console log     rows 1     console log     rows 2         use map to apply spread operator to each iterable console log     cube  map function iterator         return     iterator         for  var row of cube        for  var value of row            console log value             Note that our custom iterable won t behave like a 2-D array in all cases  for example  we haven t implemented a map   function  This answer shows how you could implement a generator map function  see here for the difference between iterators and generators  also  generators are an ES2016 feature  not ES2015  so you ll need to change your babel presets if you re compiling with babel

User · Answer

Try this   var i  j   for  i   0  i  lt  cubes length  i          for  j   0  j  lt  cubes i  length  j             do whatever with cubes i  j

User · Answer

You can do something like this   var cubes       1  2  3     4  5  6         7  8  9       for var i   0  i  lt  cubes length  i          var cube   cubes i       for var j   0  j  lt  cube length  j              display  cube     i          j            cube j              Working jsFiddle    http   jsfiddle net TRR4n    The output of the above   cube 0  0    1 cube 0  1    2 cube 0  2    3 cube 1  0    4 cube 1  1    5 cube 1  2    6 cube 2  0    7 cube 2  1    8 cube 2  2    9

User · Answer

JavaScript does not have such declarations   It would be   var cubes         regardless  But you can do   for var i   0  i  lt  cubes length  i        for var j   0  j  lt  cubes i  length  j                 Note that JavaScript allows jagged arrays  like        1  2  3      1  2  3  4      since arrays can contain any type of object  including an array of arbitrary length   As noted by MDC       for  in should not be used to iterate over an Array where index order   is important    If you use your original syntax  there is no guarantee the elements will be visited in numeric order

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Or you can do this alternatively with  forEach      var cubes       1  2  3     4  5  6         7  8  9       cubes forEach function each item      if  Array isArray item            If is array  continue repeat loop     item forEach each       else       console log item             If you need array s index  please try this code   var i   0  j   0   cubes forEach function each item      if  Array isArray item            If is array  continue repeat loop     item forEach each       i        j   0      else       console log       i          j            item       j              And the result will look like this    0  0    1  0  1    2  0  2    3  1  0    4  1  1    5  1  2    6  2  0    7  2  1    8  2  2    9

User · Answer

An efficient way to loop over an Array is the built-in array method  map    For a 1-dimensional array it would look like this   function HandleOneElement  Cuby        Cuby dimension    Cuby position x          cubes map HandleOneElement       the map function will pass each element   for 2-dimensional array   cubes map  function  cubeRow     cubeRow map  HandleOneElement         for an n-dimensional array of any form   Function prototype ArrayFunction   function param      if  param instanceof Array        return param map  Function prototype ArrayFunction  this           else return  this  param      HandleOneElement ArrayFunction cubes

[javascript] For loop in multidimensional javascript array

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