GFact | Does JavaScript guarantee object property order?

There is a quite popular query about whether Java Script guarantees object property order or not. Here, in this article let us know about this famous query in detail.

Does JavaScript guarantee object property order?

If we create an object for example:

var obj = {};obj.prop1 = “Foo”;obj.prop2 = “Bar”;

Will the resulting object always look like this?

{ prop1 : “Foo”, prop2 : “Bar” }

Will the properties be in the same order that we added them? Well we will discuss about this in the following case:

Does JavaScript guarantee object property order?

“NO”, JavaScript does not guarantee the order of object properties. In most programming languages, objects are implemented as collections of key-value pairs, and the order of these pairs is not typically guaranteed.

However, starting with ECMAScript 2015 (ES6), JavaScript introduced a guarantee for the order of object properties in certain cases. Specifically, when you iterate over the properties of an object using a ‘for…in‘ loop or the ‘Object.keys()’, ‘Object.values()’, or ‘Object.entries()’ methods, the order of properties is guaranteed to be the same as the order in which they were added to the object.

Here’s an example code for the above property:

Javascript

const myObject = { b: 2, a: 1, c: 3 };

for (const key in myObject) {
  console.log(key);
  // Output: 'b', 'a', 'c' (order may vary in some JavaScript engines)
}

console.log(Object.keys(myObject));
// Output: ['b', 'a', 'c'] (order may vary in some JavaScript engines)

Output

b
a
c
[ 'b', 'a', 'c' ]

Note: Order may vary in some Java Script engines

However, it’s important to note that this order guarantee is relatively recent and is not universally supported across all JavaScript engines or environments.

In practice, many developers still consider the order of object properties to be unpredictable and do not rely on it for their code. If you need a specific order for your data, it’s better to use an array or another data structure explicitly designed for ordered collections.