Retrieving properties from item in array by string in javascript

Question

So I know I can retrieve properties from an object by string with bracket notation:

const obj = {a:[
  {b: 'hi'},
]};

console.log(obj['a']); // Array [Object { b: "hi" }]

But if I try to access the item in the array with that notation, it doesn't allow it:

console.log(obj['a[0].b']);  // undefined
console.log(obj['a[0]']);    // undefined

Is there a way to do this in javascript?

Why am I doing this?

So my function is getting strings with array and object information like this:

"folder[2].people[1].name.firstName"
"folder[2].people[1].name.lastName"
"folder[2].name"

and I need to get that information from the object itself. I'd prefer to not have to parse the string.

There is no a[0] as a property/key, that's why you get the error. Your object prop a is an array of objects. — Robert
– Robert, Commented May 13, 2021 at 20:56

germanio · Accepted Answer · 2021-05-13 21:05:14Z

1

Have you tried using... eval()? (more info here)

WARNING: Never use eval()! (read this)

const obj = {
  a: [
    { b: 'hi' },
  ]
};
console.log(eval('obj.a[0].b'));
// prints "hi"

answered May 13, 2021 at 21:05

germanio

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Comments

Prosy A. · Accepted Answer · 2021-05-13 20:54:26Z

1

Use this: console.log(obj['a'][0].b);

 const obj = {a:[
  {b: 'hi'},
]};
console.log(obj['a'][0].b);

answered May 13, 2021 at 20:54

Prosy A.

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Comments

mykaf · Accepted Answer · 2021-05-13 20:55:09Z

1

You're combining all your keys into a single string so it's looking for a key that matches that string.

Try

console.log(obj['a'][0])
console.log(obj['a'][0]['b'])

answered May 13, 2021 at 20:55

mykaf

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Comments

FlYiNGPoTAToChiP · Accepted Answer · 2021-05-13 22:32:37Z

0

if you run it on the browser console(F12) it will be very clear

when you do obj['a'] it already return the array [{ b: 'hi' },]
then you get b by [{ b: 'hi' },][0].b
so the correct way is obj['a'][0].b

obj['a[0]'] means you trying to get

obj = { 
  'a[0]':??? // <= this
};

which doesn't exist

const obj = {a:[
    {b: 'hi'},
  ]};
console.log("obj['a'] = ", obj['a']);
console.log("obj['a'][0] = ", obj['a'][0]);
console.log("obj['a'][0].b = ", obj['a'][0].b);

obj = {'a[0]':"test"};
console.log(obj['a[0]']);

edited May 13, 2021 at 22:32

answered May 13, 2021 at 21:43

FlYiNGPoTAToChiP

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Retrieving properties from item in array by string in javascript

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WARNING: Never use eval()! (read this)

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