How to keep the sequence in javascript Map?

Question

i have myData map as below

 var myData =  new Object();

 myData[10427] = "Description 10427";
 myData[10504] = "Description 10504";
 myData[10419] = "Description 10419";

but now when i iterate over myData, i don't get same sequnce in chrome and IE works fine in firefox. It iterates in ascending order of key

for (var key in myData) {
  alert("key is"+key);
  }

i get the output in ascending order in alert as 10419,10427,10504

How i can make sure to iterate in same order as data as inserted in map?

Use a string instead of a number. Something like myDate['10427'] = "Description 10427";. If you just use a number it gets added at that index in the array. — putvande
– putvande, Commented Jul 17, 2013 at 9:48
@putvande — Nonsense. The value you pass to square bracket notation will be stringified before use. Plain objects are always unordered. — Quentin
– Quentin, Commented Jul 17, 2013 at 9:48
Ow my bad... I thought the question was about an Array. Misread it. — putvande
– putvande, Commented Jul 17, 2013 at 10:07

Mamtha Soni K · Accepted Answer · 2018-06-14 17:27:23Z

64

ES6 Maps preserves the insertion order.

The set method is used for setting the key value pairs

var myData = new Map();
myData.set(10427, "Description 10427");
myData.set(10504, "Description 10504");
myData.set(10419, "Description 10419");

Map keys and values are printed using

myData.forEach((value,key) => console.log(key, value));

This will print the keys and values in the insertion order

answered Jun 14, 2018 at 17:27

Mamtha Soni K

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2 Comments

Ken Lin Over a year ago

"The Map object holds key-value pairs and remembers the original insertion order of the keys." developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…

Sathiamoorthy Over a year ago

Console.log it printed insertion order, but while iterating in HTML, it not maintaining the insertion order.

Quentin · Accepted Answer · 2013-07-17 09:48:32Z

8

Objects are unordered in JS. Use an array if order matters.

var myData = [];
myData.push({ "number": 10427, description: "Description 10427" });

answered Jul 17, 2013 at 9:48

Quentin

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4 Comments

emilly Over a year ago

i do not want the order i want the same sequence(while iteration) as the sequnce of data insertion

Quentin Over a year ago

If you want them in insertion order, then don't sort them.

emilly Over a year ago

i am not sorting them. They are getting automatically in chrome and ie but works fine in firefox

Quentin Over a year ago

If you want them in insertion order, then store them in an array as per this answer and don't sort the array.

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