In JavaScript, do there exist any ways to get a property of an object without using dot notation or bracket notation?

Question

Let's say I have a simple object a = {b: 2} . I know of two ways to get the value of property b of a:

Dot notation: ab // 2

and

Bracket Notation: a['b'] // 2

Practicality aside, does there exist any way to get the value of b from object a without using either of these two methods (dot notation and bracket notation)? MDN's page on Property Accessors only lists the 2 methods.

---

It's just a curiosity I had. I know there exist obscure ways to call functions without parenthesis, eg

parseInt`5.1`

I wanted to see if a similarly obscure thing was possible for Property access.

Answer 1

First thing that springs to mind is Object.values

 const a = {b: 2} Object.values(a).forEach(v => { console.info(v) }) 

But how would you know what key you're accessing?

There's also Object.entries() I suppose

 const a = {b: 2} Object.entries(a).forEach(entry => { // entries are [key, value] arrays let value = entry.pop() let key = entry.pop() console.info(key, ':', value) }) 

Note: I used Array.prototype.pop() so as not to use "bracket notation" .

Answer 2

This is not exactly the same as accessing a property, but it's nevertheless a sneaky way to get at an object's contents if you are using the latest JS (es6+). All the hip JS kids are doing it these days.

const { b } = a
console.log(b) // 2

This is called destructuring , it works with objects and arrays, and you can read more about it here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment

Answer 3

Don't forget Object.getOwnPropertyDescriptor() :

const object1 = {
  property1: 42
}

const descriptor1 = Object.getOwnPropertyDescriptor(object1, 'property1');
console.log(descriptor1.value);//42

It doesn't search through the prototype chain, but it works on immediate properties and worth noting, for you can make recursive functions searching the prototype chain with it :)

Answer 4

Here's an implementation of lodash 'get' and 'set' without using dot or bracket notation; useful for passing security scans.

https://jsfiddle.net/5amtL8zx/17/

/* lodash implementation of 'get', 'set', and 'unset' without dot or bracket notation
  * - supports getting and setting 'prop1.2' array element but not with brackets: 'prop1.[2]'
  */
isObjectKey = (obj, key) => {
  return Object.getPrototypeOf(obj) === Object.prototype && /string|number/.test(typeof key);
}

isArrayNumber = (obj, key) => {
  const isKey = /string|number/.test(typeof key), path = isKey ? String(key).split('.') : [], prop = isKey && path.length > 1 ? path.shift() : '';
  return Object.getPrototypeOf(obj) === Array.prototype && isKey && !isNaN(prop);
}

isValid = (obj, key) => {
  const isObj = isObjectKey(obj, key), isArr = isArrayNumber(obj, key);
  return isObj || isArr;
}

define = (obj, key, value) => {
  Object.defineProperty(obj, String(key), { value, writable: true, configurable: true, enumerable: true  });
}

get = (obj, key, value) => {
  if (!isValid(obj, key)) {
    return undefined;
  }
  let path = String(key).split('.'), prop = path.shift(), result = new Map(Object.entries(obj)).get(prop);
  return path.length && typeof result !== 'undefined' ? get(result, path.join('.'), value) : result || value;
}

set = (obj, key, value) => {
  if (!isValid(obj, key)) {
    return undefined;
  }
  let path = key.split('.'), prop = path.shift();
  if (!(prop in obj)) {
    define(obj, prop, {});
  }
  const result = get(obj, prop);
  return path.length && isValid(result, path.join('.')) ? set(result, path.join('.'), value) : define(obj, prop, value);
}

unset = (obj, key) => {
  if (!isValid(obj, key)) {
    return undefined;
  }
  let path = key.split('.'), prop = path.shift();
  if (!(prop in obj)) {
    return undefined;
  }
  if (path.length) {
    let result = get(obj, prop);
    result = unset(result, path.join('.'));
    set(obj, prop, result);
    return obj;
  } else {
    const { [prop]: remove, ...rest } = obj;
    return rest;
  }
}

let obj = {};
set(obj, 'prop1.prop2', 'value1');
console.log(Object.entries(obj));
console.log(get(obj, 'prop1.prop2'));
const prop1 = get(obj, 'prop1');
set(prop1, 'prop2', 'value2');
console.log(get(obj, 'prop1.prop2'));
set(obj, 'prop3', [1, 2, 3]);
console.log(get(obj, 'prop3'));
console.log(get(obj, 'prop3.2'));
console.log(get(obj.prop3, 0));
set(obj, 'prop3.3', 4);
console.log(get(obj, 'prop3.3'));
set(obj, 'prop4', [{'name': 'Bob'}]);
console.log(get(obj, 'prop4.0'));
unset(obj, 'prop4.0.name')
console.log(get(obj, 'prop4.0'));
//[["prop1", {
//  prop2: "value1"
//}]]
//"value1"
//"value2"
//[1, 2, 3]
//3
//1
//4
//{
//  name: "Bob"
//}
//{ ... }