Using an integer as a key in an associative array in JavaScript

Question

When I create a new JavaScript array  and use an integer as a key  each element of that array up to the integer is created as undefined  For example  var test   new Array    test 2300     Some string   console log test    will output 2298 undefined s and one  Some string   How should I get JavaScript to use 2300 as a string instead of an integer  or how should I keep it from instantiating 2299 empty indices

User · Answer

Get the value for an associative array property when the property name is an integer:

Starting with an associative array where the property names are integers:

var categories = [
    {"1": "Category 1"},
    {"2": "Category 2"},
    {"3": "Category 3"},
    {"4": "Category 4"}
];

Push items to the array:

categories.push({"2300": "Category 2300"});
categories.push({"2301": "Category 2301"});

Loop through the array and do something with the property value.

for (var i = 0; i < categories.length; i++) {
    for (var categoryid in categories[i]) {
        var category = categories[i][categoryid];
        // Log progress to the console
        console.log(categoryid + ": " + category);
        //  ... do something
    }
}

Console output should look like this:

1: Category 1
2: Category 2
3: Category 3
4: Category 4
2300: Category 2300
2301: Category 2301

As you can see, you can get around the associative array limitation and have a property name be an integer.

NOTE: The associative array in my example is the JSON content you would have if you serialized a Dictionary<string, string>[] object.

User · Answer

As people say  JavaScript will convert a string of number to integer  so it is not possible to use directly on an associative array  but objects will work for you in similar way I think  You can create your object  var object        And add the values as array works  object 1    value  object 2    value   This will give you       1   value     2   value    After that you can access it like an array in other languages getting the key  for key in object       value   object key       I have tested and works

User · Answer

If the use case is storing data in a collection then ECMAScript  6 provides the Map type  It s only heavier to initialize  Here is an example  const map   new Map    map set 1   quot One quot    map set 2   quot Two quot    map set 3   quot Three quot     console log  quot     With Map     quot     for  const  key  value  of map        console log    key     value     typeof key          console log  quot     With Object     quot     const fakeMap         1   quot One quot       2   quot Two quot       3   quot Three quot      for  const key in fakeMap        console log    key     fakeMap key      typeof key          Result      With Map     1  One  number  2  Two  number  3  Three  number      With Object     1  One  string  2  Two  string  3  Three  string

User · Answer

Compiling other answers  Object var test        When using a number as a new property s key  the number turns into a string  test 2300     Some string   console log test  2300        Output   Some string   When accessing the property s value using the same number  the number is turned into a string again  console log test 2300       Output   Some string   When getting the keys from the object  though  they aren t going to be turned back into numbers  for  var key in test        console log typeof key        Output   string   Map ECMAScript 6 allows the use of the Map object  documentation  a comparison with Object   If your code is meant to be interpreted locally or the ECMAScript  6 compatibility table looks green enough for your purposes  consider using a Map  var test   new Map    test set 2300   Some string    console log test get 2300       Output   Some string   No type conversion is performed  for better and for worse  console log test get  2300        Output  undefined test set  2300    Very different string    console log test get 2300       Output   Some string

User · Answer

You can just use an object   var test      test 2300     Some string

User · Answer

Use an object - with an integer as the key - rather than an array

User · Answer

Use an object instead of an array   Arrays in JavaScript are not associative arrays   They are objects with magic associated with any properties whose names look like integers   That magic is not what you want if you re not using them as a traditional array-like structure   var test       test 2300     some string   console log test

User · Answer

Use an object  as people are saying  However  note that you can not have integer keys  JavaScript will convert the integer to a string  The following outputs 20  not undefined   var test      test 2300    20  console log test  2300

User · Answer

Try using an Object  not an Array   var test   new Object    test 2300     Some string

User · Answer

Sometimes I use a prefixes for my keys  For example  var pre    foo       key   pre   1234  obj        obj key    val   Now you don t have any problem accessing them

[javascript] Using an integer as a key in an associative array in JavaScript

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