How to get first key pair element of JSON object without knowing key and deleting it in node red [duplicate]

Question

I am writing a function node in node-red that is taking in a JSON object with arbitrary key val pairs:

{ 30000c690b61: "m8Jp_M7Lc0",
  30000c290bdc65: "S3qg3Rkl8Y", 
  30000c290bdf1c: "KsLpfVrR4W", 
  30000c290be5d0: "oXasuCWV_q", 
  30000c29e618: "6Q67v-gJkS" … }

I would like to access the first key pair element in this object, store it, and then delete it. I have tried multiple things, but since it is node-red, it seems to behave different

It might be helpful to show one of the things you've tried, and how the behavior differed between node-red and another JS environment. — apsillers
– apsillers, Commented Feb 7, 2017 at 18:24
it is not a duplicate, since that link you posted answers about a key that is known - I would just like to remove the first element ( I cant just do delete myObject[30000c690b61 ]; since the key always changes... — Sharon Soleman
– Sharon Soleman, Commented Feb 7, 2017 at 18:29
Ive tried getting the first element using [0], or doing a for loop to get the first key and val, but both didnt work — Sharon Soleman
– Sharon Soleman, Commented Feb 7, 2017 at 18:32
You want to delete the item you just stored from where you stored it? Or do you mean you want to delete it from the original JSON object, not the stored location? — TylerH
– TylerH, Commented Jul 29 at 20:40

Vladu Ionut · Accepted Answer · 2017-02-07 18:34:13Z

34

var firstKey = Object.keys(myObject)[0];
delete myObject[firstKey ];

answered Feb 7, 2017 at 18:34

Vladu Ionut

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Comments

apsillers · Accepted Answer · 2017-02-07 18:49:57Z

15

Getting the "first" element of a JSON object expression is difficult, since JSON objects are not intended to be ordered collections. They are "ordered" in JSON only because they must have a string serialization that is an ordered sequence of characters, but two JSON object expressions with differently-ordered properties are meant to convey identical semantics.

If you are willing to trust your JavaScript environment to preserve the ordering of keys when iterating (which is not an assumption defined in the ECMAScript spec, but may be true in your environment's implementation), you can do:

var myObj = JSON.parse("{ ... }");
var firstKey = Object.keys(myObj)[0];
delete myObj[firstKey];

If you do not want to make such an unsafe assumption, you need to read the JSON string and manually determine the key name between the first set of quotation marks. This involves some effort, because you must also handle escaped quotation marks that may appear within the key name itself.

edited Feb 7, 2017 at 18:49

answered Feb 7, 2017 at 18:36

apsillers

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1 Comment

Sharon Soleman Over a year ago

thank you. and yes, i will have to look into that since i do need to ensure that ordering is ensured.

Fayiz TP · Accepted Answer · 2022-10-10 14:04:34Z

1

const defaultvalue =yourObject[Object.keys(yourObject).at(0)]

To get first element from JSON Object

answered Oct 10, 2022 at 14:04

Fayiz TP

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Comments

dna123 · Accepted Answer · 2023-06-02 12:08:55Z

1

first_key = next(iter(json))
first_value = json[first_key]

edited Jun 2, 2023 at 12:08

answered Jun 2, 2023 at 12:08

dna123

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2 Comments

chrslg Over a year ago

Please avoid code only answer, and add some explanation. Especially when answering to old questions, it is important to explain why your answer is different, and even better than existing answers.

the Tin Man Over a year ago

Please read "How to Answer" and "Explaining entirely code-based answers". It helps more if you supply an explanation why this is the preferred solution and explain how it works. We want to educate, not just provide code.

Thilak · Accepted Answer · 2017-02-07 18:44:16Z

0

The Following Code will get First element key pair from the JSON Object and Delete It.

var resultJSON = '{ "30000c690b61": "m8Jp_M7Lc0",
  "30000c290bdc65": "S3qg3Rkl8Y", 
  "30000c290bdf1c": "KsLpfVrR4W", 
  "30000c290be5d0": "oXasuCWV_q", 
  "30000c29e618": "6Q67v-gJkS"}';
var result = $.parseJSON(resultJSON);
$.each(result, function(k, v) {
  //display the key and value pair
  alert(k + ' is ' + v);
  //For Delete the first key pair
   delete result['k'];
  exit;
});

answered Feb 7, 2017 at 18:44

Thilak

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Comments

Jan · Accepted Answer · 2025-07-29 14:55:39Z

-1

This should be the fastest.

var src = json()
for (var stKey in src) break;

var log = `Deleting ${stKey}:${src[stKey]}\n`

delete src[stKey];

console.log(log + JSON.stringify(src, null, 2));

function json() {
  return {
    "30000c690b61": "m8Jp_M7Lc0",
    "30000c290bdc65": "S3qg3Rkl8Y",
    "30000c290bdf1c": "KsLpfVrR4W",
    "30000c290be5d0": "oXasuCWV_q",
    "30000c29e618": "6Q67v-gJkS"
  };
}

answered Jul 29 at 14:55

Jan

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