Symbol Type

Question 1

By specification, only two primitive types may serve as object property keys:

Answer 1

string type,

symbol type.

Question 2

A _______ represents a unique identifier.

Answer 2

“symbol”

Question 3

let id1 = Symbol(“id”);
let id2 = Symbol(“id”);

alert(id1 == id2); // Returns and why?

Answer 3

false

Symbols are guaranteed to be unique.

Question 4

let id1 = {};
let id2 = {};

alert(id1 == id2); returns

Answer 4

false

Question 5

let id1 = {};
let id2 = id1;

alert(id1 == id2); returns?

Answer 5

true

Question 6

Symbols do or don’t auto-convert to a string

Answer 6

don’t

Question 7

let id = Symbol(“id”);
alert(id); // returns?

Answer 7

TypeError: Cannot convert a Symbol value to a string

Question 8

let id = Symbol(“id”);
alert(id.toString()); // returns

Answer 8

Symbol(id), now it works

Question 9

let user = { // belongs to another code
name: “John”
};

let id = Symbol(“id”);

// assign id to user object

alert( user[id] ); // we can access the data using the symbol as the key

Answer 9

user[id] = 1;

Question 10

If we want to use a symbol in an object literal {…}

Answer 10

we need square brackets around it.

Question 11

let id = Symbol(“id”);

let user = {
name: “John”,
// code here
};

what is correct [id]: 123 or [“id”]:123 and why?

Answer 11

That’s because we need the value from the variable id as the key, not the string “id”.

Question 12

Symbolic properties do not participate in_________ loop

Answer 12

for..in loop.

Question 13

let id = Symbol(“id”);
let user = {
name: “John”,
age: 30,
[id]: 123
};

for (let key in user) alert(key); // returns?

Answer 13

name, age (no symbols)

Question 14

let id = Symbol(“id”);
let user = {
[id]: 123
};

let clone = Object.assign({}, user);

alert( clone[id] ); // returns

Answer 14

123

Question 15

Symbols are always different values, even if they have the same name. If we want same-named symbols to be equal, then we should use the global registry:__________ returns (creates if needed) a global symbol with key as the name

Answer 15

Symbol.for(key)

Question 16

let sym = Symbol.for(“name”);
// get name by symbol

alert( ); // name

Answer 16

Symbol.keyFor(sym)

Question 17

let sym2 = Symbol.for(“id”);

alert( ); // id

Answer 17

Symbol.keyFor(sym2)