W3

Question 1

create an object named “obj” with data members “property_1: value_1” and “property_2:value_2” using object literal notation

Answer 1

var obj = { property_1:   value_1,   
            property_2:   value_2
};

Question 2

Add a function named “setAge” that sets the age of the object using the “newAge” parameter

var obj = { property_1:   value_1,   
            property_2:   value_2,   
            // ...,
            "property n": value_n };

Answer 2

setAge: function(newAge){this.age = newAge}

Question 3

Use the built in “Object.create()” function to create a new instance of an “architect” object named “architect1”

Answer 3

var architect1 = Object.create(architect);

Question 4

call the “setName” function on an architect object named “arch2”. Set the name to “Mary”

Answer 4

arch2.setName(“Mary”);

Question 5

create an “architect” object using a function constructor with the properties name, age, and occupation. inName and inAge are passed as arguments

Answer 5

function architect(inName, inAge){
    this.name = inName;
    this.age = inAge;
    this.occupation = "architect";
}

Question 6

Use the architect function prototype to create a new method “setName” that takes the parameter “newName”

Answer 6

architect.prototype.setName = function(newName){this.name = newName};

Question 7

Why won’t this code output the architect’s name property?

architect.prototype.outputNameDelay = function(){
    setTimeout(function(){
    console.log(this.name);
    },1000);
}
// ...
architect2.outputNameDelay(); // outputs undefined

Answer 7

Because the “this” keyword is within the function scope of the “setTimeout” function, which isn’t a method of the architect object

To resolve this, we can create a function variable named “that” and initialize it to “this”. We can also use function arrow syntax.

Question 8

Differences between initializing with var, let, and const

Answer 8

var : Scope is its current execution content (function scope if declared within a function, or global outside any function)

let: block scope
const: block scope, unmodifiable value

Question 9

create a constructor within this class that sets the name and age of the object

class architect{

name;
age;
occupation = "architect"; // default value of "architect" for occupation

// CONSTRUCTOR HERE

setName(newName){this.name = newName}

setAge(newAge){this.age = newAge}

getName(){return this.name;}

getAge(){return this.age;}

}

Answer 9

constructor(setName = “”, setAge = 0){ // handle missing parameters
this.name = setName;
this.age = setAge;
}

Question 10

Properties within classes are public by default. How do we declare a property as private?

Answer 10

Use the prefix ‘#’ before the identifier

Question 11

How to catch an exception on a block of code

Answer 11

Use a try catch block. Example:

const PI = 3.14159;

console.log(“trying to change PI!”);

try{
    PI = 99;
}catch(ex){
    console.log("uh oh, an error occurred!");
}

console.log(“Alas, it cannot be done, PI remains: “ + PI); // This code runs successfully

Question 12

Output an error message within a catch block

try{
    PI = 99;
}catch(ex){
  // Code here
}

Answer 12

console.log(ex.message);

Question 13

How to execute code in a try catch block regardless of if the code runs successfully

Answer 13

add a “finally” block

ex.

try{
    PI = 99;
}catch(ex){
    console.log("uh oh, an error occurred: " + ex.message); 
    // outputs: uh oh, an error occurred: Assignment to constant variable.
}finally{
    console.log("always execute code in this block");
}

Question 14

How to create a custom exception with an error message

Answer 14

use the throw keyword

ex.
    if(y == 0){
    throw new Error("Division by Zero!");
    }

Question 15

How to guarantee the order of execution in a program (have functions run in the intended order)

Answer 15

Use the “promise” keyword within a function, then call the function followed by the “then” keyword

ex.

// output "A" after a random time between 0 & 3 seconds
function outputA(){
    var randomTime = Math.floor(Math.random() * 3000) + 1;

    return new Promise(function(resolve, reject){ // place our code inside a "Promise" function
        setTimeout(function(){
            console.log("A");
            resolve(); // call "resolve" because we have completed the function successfully
        },randomTime);
    });   
}

// call the outputA function and when it is “resolved”, output a confirmation to the console

outputA().then(function(){
console.log(“outputA resolved!”);
});

Question 16

How to return data after a Promise

Answer 16

Pass the data to the resolve object, and output the data message

ex.
function outputA(){
    var randomTime = Math.floor(Math.random() * 3000) + 1;

    return new Promise(function(resolve, reject){ // place our code inside a "Promise" function
        setTimeout(function(){
            console.log("A");
            resolve("outputA resolved!"); // call "resolve" because we have completed the function successfully
        },randomTime);
    });   
}

// call the outputA function and when it is “resolved”, output a confirmation to the console

outputA().then(function(data){
console.log(data);
});

Question 17

What keyword can we use in a promise if the function is not guaranteed to execute?

Answer 17

We can use “reject” instead of “resolve” and output the reason within a catch block

ex.

function outputA(){
    var randomTime = Math.floor(Math.random() * 3000) + 1;

    return new Promise(function(resolve, reject){ // place our code inside a "Promise" function
        setTimeout(function(){
            console.log("-");
            reject("outputA rejected!"); // call "reject" because the function encountered an error
        },randomTime);
    });   
}

// call the outputA function and when it is “resolved” or “rejected, output a confirmation to the console

outputA()
.then(function(data){
    console.log(data);
})
.catch(function(reason){
    console.log(reason);
});

Question 18

How can we chain together Promise objects to execute one after the other?

Answer 18

using the “then” keyword

ex.

outputA()
.then(outputB)
.then(outputC)

Question 19

syntax for arrow functions:

Answer 19

parameter => logic

Question 20

When are arrow functions most useful when trying to simplify the syntax?

Answer 20

When the function takes no parameters.

ex.

var outputMessage = function() {
    console.log("Hello Function Expression");
};

// is the same as:

var outputMessageArrow = () => console.log(“Hello Arrow Function”);

Question 21

Explain these features of arrow functions:

Implicit return statement
Lexical “this”

Answer 21

Implicit return statement:
returns the value of the statement, without having to use the “return” keyword

ex.
var adderArrow = (num1, num2) => num1 + num2;

Lexical “this”: Uses the “this” value of the parent scope.

ex.
architect.prototype.outputNameDelay = function(){
setTimeout(() => { console.log(this.name); }, 1000);
};