Object fields sequence

Question

I have a JavaScript object written in javascript code as below:

var rtnStr = {"000":"area000","020":"area020","030":"area030",
              "040":"area040","047":"area047","049":"area049",
              "050":"area050","060":"area060","070":"area070",
              "100":"area100", "900":"area900"};

for (var key in rtnStr) {
  document.write('rtnStr[' + key + ']= ' + rtnStr[key] + '<br />');
}

then I run the code in browser, I got the result:

rtnStr[100]= area100
rtnStr[900]= area900
rtnStr[000]= area000
rtnStr[020]= area020
rtnStr[030]= area030
rtnStr[040]= area040
rtnStr[047]= area047
rtnStr[049]= area049
rtnStr[050]= area050
rtnStr[060]= area060
rtnStr[070]= area070

the object fields(keys) sequence is not the same as I have declare, How can I got the result as below?

rtnStr[000]= area000
rtnStr[020]= area020
rtnStr[030]= area030
rtnStr[040]= area040
rtnStr[047]= area047
rtnStr[049]= area049
rtnStr[050]= area050
rtnStr[060]= area060
rtnStr[070]= area070
rtnStr[100]= area100
rtnStr[900]= area900

possible duplicate of [Elements order in a "for (… in …)" loop](http://stackoverflow.com/questions/280713/elements-order-in-a-for-in-loop) — VisioN, Dec 17 '13 at 13:17

score 1 · Answer 1 · answered Dec 17 '13 at 13:17

JavaScript objects are unordered.

If you want to output their properties in a sorted order then:

Create an array
Loop over the object, pushing the property names into the array
Sort the array
Loop over the array (and use the values to access the original object).

score 0 · Answer 2 · answered Dec 17 '13 at 13:23

 var rtnStr = {"000":"area000","020":"area020","030":"area030",
              "040":"area040","047":"area047","049":"area049",
              "050":"area050","060":"area060","070":"area070",
              "100":"area100", "900":"area900"};

  array_ = [];

  for (var key in rtnStr) {
    array_.push(key)
  }

  array_.sort();


  for (var key in array_) {
    document.write('rtnStr[' + key + ']= ' + rtnStr[key] + '<br />');
  }

Tibos · Answer 3 · 2013-12-17T13:28:49.967

As mentioned by @Quentin, the order of the properties in JavaScript objects is undefined. The spec doesn't even mention if the properties will be returned in the same order by different for..ins.

What you can do is get the keys in an array and sort them:

var rtnStr = {"000":"area000","020":"area020","030":"area030",
              "040":"area040","047":"area047","049":"area049",
              "050":"area050","060":"area060","070":"area070",
              "100":"area100", "900":"area900"};

var keys = Object.keys(rtnStr).sort().forEach(function(key){
  document.write('rtnStr[' + key + ']= ' + rtnStr[key] + '<br />');
});

MDN has a page for Object.keys where you can find the browsers it works on and a polyfill for those it doesn't.

One thing to note is that your initial version of the code iterates over inherited properties as well. That is generally considered to be unsafe and Object.keys doesn't exhibit that behavior.

Object fields sequence

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