Object methods, "this"

Question 1

let user = {
name: “John”,
age: 30
};

// write a function expression that outputs the below

user.sayHi(); // Hello!

Answer 1

user.sayHi = function() {
alert(“Hello!”);
};

Question 2

A function that is a property of an object is called its _____.

Answer 2

method

Question 3

let user = {
};

function sayHi() {
alert(“Hello!”);
}

// add the function as a method to return the below

user.sayHi(); // Hello!

Answer 3

user.sayHi = sayHi;

Question 4

Write the below as a shorthanded

user = {
sayHi: function() {
alert(“Hello”);
}
};

Answer 4

user = {
sayHi() {
alert(“Hello”);
}
};

Question 5

let user = {
name: “John”,
age: 30,

sayHi() {
alert( user.name );
}

};

let admin = user;
user = null;

admin.sayHi(); // returns and why?

Answer 5

TypeError: Cannot read property ‘name’ of null

If we decide to copy user to another variable, e.g. admin = user and overwrite user with something else, then it will access the wrong object.

Question 6

function sayHi() {
alert(this);
}

sayHi(); // returns?

Answer 6

undefined

Question 7

let user = { name: “John” };
let admin = { name: “Admin” };

function sayHi() {
alert( this.name );
}

user.f = sayHi;
admin.f = sayHi;

user.f(); //
admin.f(); //

Answer 7

John (this == user)
Admin (this == admin)

Question 8

Arrow functions have no ______

Answer 8

this

Question 9

function makeUser() {
return {
name: “John”,
ref: this
};
}

let user = makeUser();

alert( user.ref.name ); // returns?

Answer 9

Error: Cannot read property ‘name’ of undefined

Question 10

function makeUser() {
return {
name: “John”,
ref: this
};
}

let user = makeUser();
alert( user.ref.name );

The above gives an error,
how to correct?

Answer 10

function makeUser() {
return {
name: “John”,
ref() {
return this;
}
};
}

let user = makeUser();
alert( user.ref().name ); // John