Variables

Question 1

var bgColor = "blue";
var textColor = "#FF9933";

var container = document.getElementById(‘container’);

container. style.background = bgColor;
container. style.color = textColor;

Formula:
document.getElementById(“selector”).style.background

Answer 1

• assigning bgColor to the value of “blue” and the textColor to “#FF9933”
• getting the element by the id of “container”
• object.property
• variable built into webpage.method.object.property

Question 2

What characters are invalid in a variable name?

Answer 2

%, @, -, cannot start with a #

Question 3

undefined vs. null

undefined == null
undefined === null

Answer 3

• undefined works as a keyword/variable
• null works as an empty value
• undefined == null —> true
• undefined === null —> false

Question 4

What will console log out in the following code?

var part1 = “Team “;

function bam() {
	var part2 = "Treehouse";
	console.log(part2);
}

bam();

Answer 4

Treehouse

Question 5

What will console log out in the following code?

var part1 = “Team “;

function bam() {
	var part2 = "Treehouse";
	console.log(part1);
}

bam();

Answer 5

Team

Question 6

What will console log out in the following code?

var part1 = “Team “;

function bam() {
	var part2 = "Treehouse";
}

bam();

console.log(part1);

Answer 6

Team

Question 7

What will console log out in the following code?

var part1 = “Team “;

function bam() {
	var part2 = "Treehouse";
	function boom() {
		var part3 = "Go ";
		console.log(part3 + part1 + part2);
	}

boom(); }

bam();

Answer 7

Go Team Treehouse

Question 8

What will console log out in the following code?

var part1 = “Team “;

function bam() {
	var part2 = "Treehouse";
}

bam();

console.log(part2);

Answer 8

ReferenceError: part2 is not defined

Question 9

Scope

Answer 9

variables can only be used within its respective curly braces

Question 10

Shadowing

Answer 10

• idea applies to variables with the same name

- if no “var” is declared, then it becomes a global variable

Question 11

What will console log out in the following code?

var person = “Jim”;

function whosGotTheFunc() {
	var person = "Andrew";
}

person = “Nick”;

whosGotTheFunc();
console.log(person);

Answer 11

Nick

Question 12

What will console log out in the following code?

var person = “Jim”;

function whosGotTheFunc() {
	person = "Andrew";
}

person = “Nick”;

whosGotTheFunc();

console.log(person);

Answer 12

Andrew

Question 13

function elevatorCloseButton(pushed) {
	if (pushed) {
		var status = "I'll close when I'm ready.";
	}
}

elevatorCloseButton(true);

Alter the ‘elevatorCloseButton’ function to follow the best practices in declaring variables within the scope of the function.

Answer 13

function elevatorCloseButton(pushed) {
	var status;
	if (pushed) {
		status = "I'll close when I'm ready.";
	}
}

elevatorCloseButton(true);

Question 14

What does it mean to shadow a variable?

Answer 14

creating a new variable that has the same name as a variable from a higher scope

Question 15

What is the correct syntax for creating a variable in JavaScript?

Answer 15

var myVariable = “some value”;

Question 16

Why is it safer to test for undefined using the typeof operator, versus testing against the undefined value?

Answer 16

the undefined value can be reassigned, causing unusual bugs

Question 17

In the following code, what value will be displayed in the alert box?

var color = “red”;

function example () {
  color = "blue";
}

example()

alert(color);

Answer 17

blue

Question 18

What is the best way to test if a variable myVar is undefined?

Answer 18

if (typeof myVar === “undefined”) {}

Question 19

In the following code, what value will be displayed in the alert box?

var color = “red”;

function example () {
  var color = "blue";
}

example()

alert(color);

Answer 19

red

Question 20

In JavaScript, a new variable scope is created when?

Answer 20

when you open a new function definition

Question 21

What is the value of color after this code is run?

var color;

Answer 21

undefined