Arrangement of JavaScript objects based on timestamp key

Question

Arrangement of JavaScript objects based on timestamp key

In JavaScript, there are specific rules that dictate the order of object properties. One interesting example caught my attention.

When a timestamp in milliseconds is used as an object property key, the ordering does not function as expected.

However, if a timestamp in seconds is used as an object property key, the ordering works properly.

var objS = {
    1600333200: 'a',
    1600419600: 'b',
    1600338600: 'c'
};
console.log('seconds', JSON.stringify(objS));


var objMs = {
    1600333200000: 'a',
    1600419600000: 'b',
    1600338600000: 'c'
};
console.log('milliseconds', JSON.stringify(objMs));

Is there an explanation for this behavior?

javascript arrays json sorting object

Answer 1

Answer №1

Historically, the sequence of properties in an object, like a map, was typically not guaranteed. However, with the adoption of the ECMAScript 2015 Language Specification, the reliability of property order has been established. Nonetheless, the sequence of keys is still not firmly guaranteed as per the JSON guideline.

If necessary, you can create your own function to arrange the keys in numerical order.

const serialize = obj =>
  `{${Object.keys(obj)
    .sort((a, b) => parseInt(a) - parseInt(b))
    .map(key => `"${key}":${JSON.stringify(obj[key])}`).join(',')}}`;

var objMs = {
  1600338600000: 'c',
  1600333200000: 'a',
  1600419600000: 'b',
};

console.log('milliseconds', serialize(objMs));

Result

milliseconds {"1600333200000":"a","1600338600000":"c","1600419600000":"b"}

Answer 2

Historically, the sequence of properties in an object, like a map, was typically not guaranteed. However, with the adoption of the ECMAScript 2015 Language Specification, the reliability of property order has been established. Nonetheless, the sequence of keys is still not firmly guaranteed as per the JSON guideline.

If necessary, you can create your own function to arrange the keys in numerical order.

const serialize = obj =>
  `{${Object.keys(obj)
    .sort((a, b) => parseInt(a) - parseInt(b))
    .map(key => `"${key}":${JSON.stringify(obj[key])}`).join(',')}}`;

var objMs = {
  1600338600000: 'c',
  1600333200000: 'a',
  1600419600000: 'b',
};

console.log('milliseconds', serialize(objMs));

Result

milliseconds {"1600333200000":"a","1600338600000":"c","1600419600000":"b"}

Arrangement of JavaScript objects based on timestamp key

Answer №1

Result

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