Ultimate Parents of Prototypes Question

JavaScript
1

I have a question about the properties of the “ultimate parent” of prototypes.
(e.g. Array.prototype, Object.prototype, Function.prototype etc.)

I was trying to figure out which properties these prototypes hold. I knew that arrays held a property of “length” and confirmed this via the following:
console.log("This is hasOwnProperty -- " + Array.prototype.hasOwnProperty('length')); //true

It of course also stands that an array must also have the property of hasOwnProperty()

However, when trying to create a list of all the properties, it did not work. I tried to create this list via the following:
let objectArr = []; for (let property in Array.prototype) { objectArr.push(property); }; console.log(objectArr);

This only return a set of empty brackets. Any help on how to access a complete list of the properties on the ultimate parent prototypes?

2

Hello and welcome to the forum :slight_smile:!

That’s because the for...in loop cannot access the non enumerable properties of an object, in this case Array (or the prototype).

You could use Object.getOwnPropertyNames(Array),

Regards!

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3

Thank you! How would you pull in the ones that are not the objects “own” properties?

4

You mean, including the parents? If so, then You would need to create a function to do something like this:

let count = 0
let obj = Array
let result = []

while (obj.prototype && count < 1000) {
  result.push(...Object.getOwnPropertyNames(obj.prototype))
  obj = obj.prototype
  count++ // Just in case xD
}

console.log(result);
// Expected result:
// [ 
//   'length',
//   'constructor',
//   'concat',
//   'copyWithin',
//   'fill',
//   'find',
//   'findIndex',
//   'pop',
//   'push',
//   'reverse',
//   'shift',
//   'unshift',
//   'slice',
//   'sort',
//   'splice',
//   'includes',
//   'indexOf',
//   'keys',
//   'entries',
//   'forEach',
//   'filter',
//   'map',
//   'every',
//   'some',
//   'reduce',
//   'reduceRight',
//   'toString',
//   'toLocaleString',
//   'join',
//   'lastIndexOf',
//   'values',
//   'flat',
//   'flatMap'
// ]
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