Object key restrictions in JavaScript

We can write without quotes not all object keys, but only those that satisfy the following restrictions: they cannot start with a number and cannot contain a hyphen, a space, or something like that.

If a string violates a constraint, then it must be enclosed in quotation marks. In the following example, part of the keys does not satisfy the conditions, and therefore they are in quotes:

let obj = {'1key': 'a', 'key-2': 'b', key3: 'c'};

Such keys can only be accessed through square brackets:

console.log(obj['1key']); console.log(obj['key-2']);

Also, accessing such a name through an object property will result in an error:

console.log(obj.1key); console.log(obj.key-2);

But the third key is valid, and we can access it in both ways:

console.log(obj['key3']); console.log(obj.key3);

Given an object:

let obj = { '1a': 1, 'b2': 2, 'с-с': 3, 'd 4': 4, 'e5': 5 };

Which keys of this object require quotes, and which don't?

Fix the errors in the following code:

let obj = { '1a': 1, 'b2': 2, 'с-с': 3, 'd 4': 4, 'e5': 5 }; console.log(obj.1a); console.log(obj.b2); console.log(obj.c-c); console.log(obj.d 4); console.log(obj.e5);