Object references and copying

Question 1

let user = { name: ‘John’ };
let admin = user;
admin.name = ‘Pete’;
alert(user.name);

// returns and why?

Answer 1

// ‘Pete’, changes are seen from the “user” reference

Question 2

let a = {};
let b = a;
alert( a == b ); // returns?

Answer 2

true, both variables reference the same object

Question 3

let a = {};
let b = a;
alert( a === b );

Answer 3

// true

Question 4

let a = {};
let b = {};
alert( a == b ); // returns and why?

Answer 4

false

And here two independent objects are not equal, even though they look alike (both are empty):

Question 5

const user = {
name: “John”
};
user.name = “Pete”;
alert(user.name); //

returns and why

Answer 5

Pete

An important side effect of storing objects as references is that an object declared as const can be modified.

Question 6

let user = {
name: “John”,
age: 30
};

let clone = {};
// copy all user properties into it for in loop

Answer 6

for (let key in user) {
clone[key] = user[key];
}

Question 7

let user = { name: “John” };
Object.assign(user, { name: “Pete” });
alert(user.name); // returns and why?

Answer 7

now user = { name: “Pete” }

If the copied property name already exists, it gets overwritten

Question 8

let user = {
name: “John”,
age: 30
};

let clone = // assign user to clone

alert(clone.name); // John
alert(clone.age); // 30

Answer 8

Object.assign({}, user);

Question 9

let user = {
name: “John”,
sizes: {
height: 182,
width: 50
}
};

alert( ); // 182
how to access 182?

Answer 9

user.sizes.height

Question 10

let user = {
name: “John”,
sizes: {
height: 182,
width: 50
}
};

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

alert( user.sizes === clone.sizes ); // returns and why?

Answer 10

// true, same object

Question 11

let user = {
name: “John”,
sizes: {
height: 182,
width: 50
}
};

user.sizes.width = 60; // returns

Answer 11

user.sizes.width = 60; // change a property from one place

Question 12

let user = {
name: “John”,
sizes: {
height: 182,
width: 50
}
};

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

alert( user.sizes === clone.sizes ); //

Answer 12

True

Question 13

The call _______clones the object with all nested properties.

Answer 13

structuredClone(object)

Question 14

let user = {
name: “John”,
sizes: {
height: 182,
width: 50
}
};

let clone = structuredClone(user);

alert( user.sizes === clone.sizes );

Answer 14

// false, different objects

Question 15

let user = {};
user.me = user;

let clone = structuredClone(user);
alert(clone.me === clone); //

returns and why?

Answer 15

true

// let’s create a circular reference:
// user.me references the user itself

Question 16

there are cases when structuredClone fails.

For instance, when an object has a________

Answer 16

function property:

Question 17

The call ___clones the object with all nested properties.

Answer 17

structuredClone(object)