JavaScript Variables and Types Syntax Quiz

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Questions and Answers

Which keyword is used to declare variables in JavaScript?

var (correct)

int

const

let

What method is used to find the largest value between two numbers in JavaScript?

round

max (correct)

abs

min

Which of the following data types is not valid in JavaScript?

Double (correct)

Null

Function

Array

What is the result of '5 + 4 + (2 * 3)' in JavaScript?

15 Signup and view all the answers

What comment syntax is used in JavaScript similar to Java?

// comment Signup and view all the answers

If a variable has not been declared and does not exist, what value does it hold in JavaScript?

'undefined' Signup and view all the answers

What does document.getElementById return in JavaScript?

The DOM object for an element with a given id Signup and view all the answers

How can you change the text inside most elements in the DOM using JavaScript?

By setting the innerHTML property Signup and view all the answers

In JavaScript, what property can be set to change the text in form controls like textboxes?

value Signup and view all the answers

What does the function changeText() in JavaScript do?

Change the style of a textbox Signup and view all the answers

Which method allows you to manipulate or initialize text in JavaScript?

changeText() Signup and view all the answers

Which CSS style property is NOT changed in the function Preetify() in JavaScript?

background color Signup and view all the answers

What type of programming is JavaScript known for?

Event-driven programming Signup and view all the answers

In JavaScript, what is used to write a JavaScript function that will run when an event occurs?

JavaScript event handler Signup and view all the answers

What is an example of an event attribute commonly used in HTML?

onchange Signup and view all the answers

How can a JavaScript function be invoked in response to a user's click on an element?

<code>onclick</code> attribute Signup and view all the answers

What is a common drawback associated with using alert windows in JavaScript?

They disrupt the user experience Signup and view all the answers

Which HTML attribute is used to set a JavaScript function as an event handler for element interactions?

<code>onclick</code> Signup and view all the answers

Study Notes

Variables

In JavaScript, variables are declared using the var keyword.
Variable types are not specified, but JavaScript has types including Number, Boolean, String, Array, Object, Function, Null, and Undefined.
The typeof operator can be used to find out a variable's type.

Number Type

Integers and real numbers are the same type in JavaScript.
Same operators are used for numbers: +, -, *, /, %, ++, --, =, +=, -=, *=, /=, %=.
Many operators auto-convert types, e.g., "2" * 3 is 6.

Comments

JavaScript comments are the same as Java comments.
There are four comment syntaxes: HTML, CSS/JS/PHP, Java/JS/PHP, and PHP.

Math Object

The Math object has methods: abs, ceil, cos, floor, log, max, min, pow, random, round, sin, sqrt, tan.
The Math object has properties: E and PI.
Examples: var rand1to10 = Math.floor(Math.random() * 10 + 1);, var three = Math.floor(Math.PI);.

Null and Undefined

null exists, but was specifically assigned an empty or null value.
undefined has not been declared, does not exist.

Document Object Model (DOM)

Most JavaScript code manipulates elements on an HTML page.
We can examine elements' state and change state.
Examples: see whether a box is checked, insert new text into a div, change styles.

Accessing Elements

document.getElementById returns the DOM object for an element with a given id.
We can change the text inside most elements by setting the innerHTML property.
We can change the text in form controls by setting the value property.

Functions

A function is a block of code that can be called multiple times from different parts of the script.
Example: function changeText() { ... }.
Functions can be used as event handlers.

Event-Driven Programming

JavaScript programs wait for user actions called events and respond to them.
This is called event-driven programming.
Example: a clickable button that pops up a "Hello, World" window.

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Description

Test your knowledge on JavaScript variables and types syntax by answering questions related to declaring variables, assigning values, and understanding data types in JavaScript. Explore concepts like loosely typed nature, types such as Number, Boolean, String, Array, Object, Function, Null, and Undefined, and identifying variable types using 'typeof'.