Podcast
Questions and Answers
JavaScript is primarily used for:
JavaScript is primarily used for:
- Creating operating systems.
- Client-side scripting to enhance web page interactivity. (correct)
- Server-side scripting to manage databases.
- Developing mobile applications exclusively.
Brendan Eich created JavaScript at Netscape in what year?
Brendan Eich created JavaScript at Netscape in what year?
- 1990
- 2005
- 1995 (correct)
- 2000
What does ECMAScript refer to in the context of JavaScript?
What does ECMAScript refer to in the context of JavaScript?
- A deprecated version of JavaScript.
- The standardized version of JavaScript. (correct)
- A JavaScript library for DOM manipulation.
- A type of comment used in JavaScript code.
When including JavaScript in an HTML document, what is considered the best practice for script placement?
When including JavaScript in an HTML document, what is considered the best practice for script placement?
Which of the following is a benefit of using external JavaScript files?
Which of the following is a benefit of using external JavaScript files?
What is the purpose of console.log() in JavaScript?
What is the purpose of console.log() in JavaScript?
Which of the following components can a JavaScript statement contain?
Which of the following components can a JavaScript statement contain?
How does JavaScript handle whitespace?
How does JavaScript handle whitespace?
What is the primary difference between an expression and a statement in JavaScript?
What is the primary difference between an expression and a statement in JavaScript?
Which of the following is an example of a string literal in JavaScript?
Which of the following is an example of a string literal in JavaScript?
Which keyword is used to declare a variable in JavaScript that can be reassigned a new value?
Which keyword is used to declare a variable in JavaScript that can be reassigned a new value?
What is the purpose of comments in JavaScript?
What is the purpose of comments in JavaScript?
What is a key characteristic of JavaScript variables?
What is a key characteristic of JavaScript variables?
Which keyword is used to declare a variable whose value cannot be changed after it's assigned?
Which keyword is used to declare a variable whose value cannot be changed after it's assigned?
What is the purpose of the typeof operator in JavaScript?
What is the purpose of the typeof operator in JavaScript?
What happens when JavaScript reaches a return statement in a function?
What happens when JavaScript reaches a return statement in a function?
What is function hoisting in JavaScript?
What is function hoisting in JavaScript?
What is lexical scope in JavaScript?
What is lexical scope in JavaScript?
What will '42' + 8 result in, and why?
What will '42' + 8 result in, and why?
What does the isNaN() function do in JavaScript?
What does the isNaN() function do in JavaScript?
JavaScript code can only be included directly within an HTML document.
JavaScript code can only be included directly within an HTML document.
In JavaScript, the innerText property is used to insert text into an HTML element with a specified ID.
In JavaScript, the innerText property is used to insert text into an HTML element with a specified ID.
The console.xml() method is the primary method for displaying output in the browser's JavaScript console.
The console.xml() method is the primary method for displaying output in the browser's JavaScript console.
In JavaScript, extra whitespace, tabs, and line breaks are significant and will cause errors.
In JavaScript, extra whitespace, tabs, and line breaks are significant and will cause errors.
In JavaScript, every statement must end with a semicolon (;).
In JavaScript, every statement must end with a semicolon (;).
In JavaScript, keywords are special characters that perform operations on operands.
In JavaScript, keywords are special characters that perform operations on operands.
In JavaScript, a function must always return a value.
In JavaScript, a function must always return a value.
In JavaScript, variables declared with const can be re-assigned new values after their initial assignment.
In JavaScript, variables declared with const can be re-assigned new values after their initial assignment.
In JavaScript, a variable's data type is declared explicitly when the variable is created.
In JavaScript, a variable's data type is declared explicitly when the variable is created.
In JavaScript, variables declared inside a function have global scope by default.
In JavaScript, variables declared inside a function have global scope by default.
In JavaScript, variables declared without any keyword, such as var, let, or const, are not automatically declared.
In JavaScript, variables declared without any keyword, such as var, let, or const, are not automatically declared.
JavaScript functions that are defined can be called or ‘invoked’ before their declaration in the code. This feature is called hoisting.
JavaScript functions that are defined can be called or ‘invoked’ before their declaration in the code. This feature is called hoisting.
A JavaScript function is executed automatically when it is defined.
A JavaScript function is executed automatically when it is defined.
In JavaScript, using single-line comments (//) is appropriate for providing detailed explanations or disabling large blocks of code.
In JavaScript, using single-line comments (//) is appropriate for providing detailed explanations or disabling large blocks of code.
In JavaScript, the typeof operator can be used to determine the data type of a variable.
In JavaScript, the typeof operator can be used to determine the data type of a variable.
In JavaScript, the keywords var, let, and const all have the same behavior regarding scope and reassignment.
In JavaScript, the keywords var, let, and const all have the same behavior regarding scope and reassignment.
The primary purpose of the parseInt() function in JavaScript is to convert any value to a floating-point number.
The primary purpose of the parseInt() function in JavaScript is to convert any value to a floating-point number.
The JavaScript expression '50' + 10 will result in the number 60.
The JavaScript expression '50' + 10 will result in the number 60.
In JavaScript, the equality operator == only compares the values of two operands, while the strict equality operator === compares both value and type.
In JavaScript, the equality operator == only compares the values of two operands, while the strict equality operator === compares both value and type.
In JavaScript, the ternary operator is a shorthand way to write single-line comments.
In JavaScript, the ternary operator is a shorthand way to write single-line comments.
Flashcards
What is Javascript?
What is Javascript?
A scripting language embedded in web browsers that enables client-side scripting, improving web page responsiveness.
What is ECMAScript?
What is ECMAScript?
Standardized version of JavaScript by Ecma International.
Javascript: Language basics
Javascript: Language basics
Syntax, keywords, operators, and built-in objects of JavaScript.
Web page interaction
Web page interaction
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Web applications
Web applications
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External Javascript File in HTML
External Javascript File in HTML
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Javascript: Keywords.
Javascript: Keywords.
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Javascript: Operators
Javascript: Operators
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Javascript: Expressions
Javascript: Expressions
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Javascript: Expression
Javascript: Expression
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Javascript: Statement
Javascript: Statement
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Number literals
Number literals
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Variable Values
Variable Values
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Loosely typed variable
Loosely typed variable
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Strongly-typed variable
Strongly-typed variable
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Javascript Variables using 'var'
Javascript Variables using 'var'
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Javascript variables using 'let'
Javascript variables using 'let'
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Javascript variables using 'const'
Javascript variables using 'const'
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Parsing failure
Parsing failure
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What is scope?
What is scope?
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Console Output for Debugging
Console Output for Debugging
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Inline JavaScript
Inline JavaScript
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What is Syntax?
What is Syntax?
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Whitespace in JavaScript
Whitespace in JavaScript
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What is a variable?
What is a variable?
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Automatically defined Javascript variables
Automatically defined Javascript variables
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What is a Javascript function?
What is a Javascript function?
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Function Arguments
Function Arguments
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Anonymous Javascript functions
Anonymous Javascript functions
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Function Hoisting
Function Hoisting
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Global Scope
Global Scope
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Local Scope
Local Scope
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parseInt()
parseInt()
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parseFloat()
parseFloat()
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String()
String()
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toString()
toString()
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Modulus (%)
Modulus (%)
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Shorthand Assignment Operators
Shorthand Assignment Operators
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Ternary operator(?:)
Ternary operator(?:)
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Javascript: Equality (===)
Javascript: Equality (===)
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Study Notes
Basics of JavaScript
- JavaScript is an object-based scripting language embedded in web browsers like Chrome, Edge, and Firefox.
- It enables client-side scripting, which enhances web page responsiveness.
- Brendan Eich created it at Netscape in 1995 as LiveScript.
- It was renamed JavaScript to capitalize on Java's popularity, but it isn't related.
- JavaScript leads to faster, more interactive, and dynamic web experiences directly in the browser.
JavaScript Evolution & Key Features
- Microsoft's introduction of JScript caused fragmentation concerns.
- In 1997, JavaScript was standardized as ECMAScript by Ecma International.
- Despite standardization, it's still known as JavaScript.
- Brendan Eich co-founded Mozilla and launched Firefox.
- Language basics include syntax, keywords, operators, and built-in objects.
- Web page interaction involves manipulating the DOM for dynamic content.
- Web applications include creating responsive web apps and handling JSON data.
Including Scripts
- JavaScript code can be directly embedded in an HTML document between
<script>tags. - To include JavaScript code directly in an HTML document it must be inserted between
<script>tags.
document.getElementById( 'message' ).innerText = 'Hello World!'
- JavaScript can be placed in the
<head>,<body>, or end of the<body>sections within an HTML document. - Placing JavaScript in the
<head>is not usually recommended, unless it's a small script. - Placing JavaScript inside the
<body>can cause page rendering delays. - Placing JavaScript at the end of the
<body>section is the best practice, as it ensures the page loads before scripts run. - JavaScript code can be written in external
.jsfiles. - External JavaScript files are included using the
<script>tag with thesrcattribute.
<script src="external_script.js"></script>
- External JavaScript files promote reusability across multiple web pages.
- External JavaScript files improve organization by separating HTML content from behavior.
- External JavaScript files allow easier maintenance since updates update all linked pages.
- The
.jsfiles should only contain JavaScript code without<script>tags.
Console Output
- JavaScript can dynamically write content into an HTML element using the innerText property to insert text into the element with the specified ID.
- Example:
document.getElementById('message').innerText = 'Hello World!'; - JavaScript can display output using a pop-up alert.
- Use
window.alert('Hello World!');to display 'Hello World!' in a dialog box. - The
console.log()method of the console object can display content in the browser's JavaScript console for debugging. - When learning JavaScript, it is better to display output in the browser's console using
console.log('Hello World!');
Making Statements
- JavaScript code comprises instructions called “statements,” generally executed top-to-bottom by the browser’s JavaScript engine.
- Statements can contain keywords, operators, values, and expressions.
- Keywords are words with special significance in the JavaScript language.
- Operators are special characters that perform operations on operands.
- Values include text strings, numbers, boolean true or false, and null.
- Expressions are units of code that produce a single value.
JavaScript Statement Termination & Readability
- In earlier JavaScript, every statement needed to end with a semicolon (;).
- Semicolons are now optional unless multiple statements are on the same line.
- Some developers prefer using semicolons for clarity.
- Whitespace (extra spaces, tabs, and line breaks) is ignored in JavaScript.
- Spacing can improve readability in JavaScript.
- Use the space bar for indenting statements, as tab spacing may be treated differently in editors.
- Example of Readable Code:
total = 100 + 200; - Examples of Less Readable Code:
total=100+200; - Expressions produce a value and are used in calculations or function returns, example expression:
(80 + 20) → 100 - Statements perform an action, like declaring variables or running loops, example statement:
let total = 300;
JavaScript Statements & Syntax
- The rules governing the JavaScript language are “syntax.”
- JavaScript statements are often grouped using curly brackets
{}inside function blocks. - These blocks allow reusable execution when required.
- Indent statements by two spaces inside curly brackets for readability.
{
statement
statement
}
JavaScript Values
- JavaScript recognizes two types of values: fixed values and variable values.
- Fixed values (literals) can be number literals or string literals
- Number literals can be integer numbers, example
100, or floating-point numbers, example3.142. - String literals are text enclosed in single
'JavaScript Fun'or double"JavaScript Fun"quotes. - Be consistent with string literals, i.e. only use single or double quotes.
JavaScript Variable Values
- Variable values are called "variables" used to store data within a script.
- Variables are created using a JavaScript keyword, for instance,
let total. - The JavaScript assignment operator (=) is used to assign a value to the variable, for instance
let total = 300. - An expression produces a single value with values and operators.
- Example Numeric Expression:
let result = (80 + 20); - Example Expression With Variables:
let total = 300;
let newTotal = (total - 200);
- Example Operators Used In Expressions:
let finalValue = (100 + 50) * 2; // 300 - JavaScript is case-sensitive, so
totalandTotalare different variables. - Comments can explain code for better readability and debugging
- Use single-line comments
//for short explanations - Use multi-line comments
/*...*/for longer explanations or disabling blocks of code. - Always use comments to explain complex logic.
- Use comments to “comment-out” lines of code to prevent execution when debugging code.
- A variable is a container which data can be stored and retrieved later.
- JavaScript variables are easier to use because they are loosely-typed.
Loosely Typed vs Strongly Typed Variables
- Strongly typed variables must declare specifics before being used, such as:
int age = 25; // Can ONLY store integers - Example languages that use strongly typed variables: Java, C++, C#
- Loosely typed variables can store any data type without prior declaration, such as:
let data = 25; // Can Store any type of data - Example language that uses loosely typed variables: JavaScript
Declaring Variables
- Variables can be declared automatically
- In this first example, x, y, and z are undeclared variables.
- They are automatically declared when first used.
- It is considered good programming practice to always declare variables before use.
x = 5;
y = 6;
z = x + y;
- Variables can be declared using
var x = 5- The
varkeyword was used in all JavaScript code from 1995 to 2015. - The
varkeyword should only be used in code written for older browsers.
- The
var x = 5;
var y = 6;
var z = x + y;
- Variables can be declared using
let x = 5- Theletandconstkeywords were added to JavaScript in 2015. - Variables declared withletcan be reassigned new values as the script proceeds - Aletvariable can be declared without a value and assigned later.
let myNumber
myNumber = 5
let z = x + y;
- Multiple variables may be declared on a single line too:
`let i,j,k; or let i = 10, j = 20`
- Variables can be declared using
const x = 5;-constare constant values and cannot be changed. - Useconstif the type should not be changed (Arrays and Objects) - Examples usingconst
const x = 5;
const y = 6;
const z = x + y;
- Use meaningful names for variables to make the script easier to understand later
- JavaScript sets the variable type for the value assigned automatically.
- Subsequent assignation of a different data type later in the script can be made to change the variable type.
- The
typeofkeyword reveals the current variable type. - A JavaScript function is a reusable block of code designed to perform a task and return a single value.
- Executing a JavaScript function happens when it's called.
JavaScript Function Syntax
- A function is defined with the
functionkeyword. - Include the function’s name.
- Include parentheses
(). - Function names can contain letters, digits, underscores, and dollar signs.
- Parameters (optional) inside the parentheses are separated by commas:
(parameter1, parameter2,...). - The function’s code goes inside curly brackets
{}. - Function arguments are values received when the function is called.
- Inside the function, arguments act as local variables.
function name(parameter1, parameter2, parameter3) {
// code to be executed
}
Function Invocation & Return
-
Function invocation happens:
- When an event occurs (e.g., a user clicks a button).
- When it is invoked (called) from JavaScript code.
- Automatically (self invoked).
-
When JavaScript reaches a
returnstatement, the function stops executing. -
If invoked from a statement, JavaScript will
returnto execute the code after the invoking statement. -
Functions often compute a return value, returned to the "caller".
let x = myFunction(4, 3);
function myFunction(a, b) {
// Function returns the product of a and b
return a * b;
}
Assigning Functions
- Assigning a named function to a variable e.g.
function add(num1, num2) {
return num1 + num2
}
let addition = add
console.log(“Result:“, addition(100,200))
- With anonymous Function Expressions:
let anon = function(num1, num2) {
return num1 + num2
}
Self-Invoking Functions
- Self-invoking functions executes example code when the script gets loaded.
(function add(num1, num2) {
return num1 + num2
})()
Function Hoisting
- JavaScript reads scripts in two sweeps:
- First Sweep: Finds function declarations and hoists them to the top.
- Second Sweep: Executes the script.
- Function declarations can be called before the function is defined eg:
console.log("Volvo“, add(100,200))
function add(num1, num2) {
return num1 + num2
}
- But Function Expressions are NOT Hoisted, the the below example will not work
console.log("Volvo“, add(100,200))
let x = function add(num1, num2) {
return num1 + num2
}
Recognizing Scope
- Scope is where a variable is accessible in a script.
- JavaScript uses lexical scope, meaning the variable’s environment decides its accessibility.
Types of Scope
- Global Scope variables are declared outside of any function
- Global Scope variables are accessible throughout the entire script.
- Potential Issue: Naming conflicts with external scripts.
let myName = ‘Ahmed';
function readName(a, b) {
console.log(myName)
}
- Local Scope variables are declared inside a function.
- Local Scope variables only exist inside that function and cannot be accessed outside that function
function readName(a, b) {
let myName = ‘Ahmed';
console.log(myName)
}
Converting Values
- JavaScript handles different data types differently.
- Mixed data types (strings and numbers) can lead to unexpected results
- Converting a string or other types to numbers is needed to perform proper mathematical operations.
- Example of Unexpected Behavior: '42' + 8 results in '428' (string concatenation, not addition).
- The value '42' is a string, but 8 is a number.
Strings to Numbers
- Strings can be converted to numbers using built-in functions like
parseInt()andparseFloat(). - These functions allow you to work with string values as numeric types in mathematical operations.
Conversion Functions
parseInt(): Converts a string to an integer (whole number).- Example:
parseInt('42') → 42 - Ignores non-numeric characters after the number.
- Example:
parseInt('42nd Street') → 42 parseFloat()Converts a string to a floating-point number.- Example:
parseFloat('42.5px') → 42.5 parseFloat('42.5abc') → 42.5(alphabetic characters are ignored).
- Example:
Handling Non-Numeric Values
- If the conversion fails, JavaScript returns
NaN (Not a Number). - Example
parseInt('Hello') → NaN - To check if a value is not a number:
isNaN(value)returnstrueif the value is not a number.
let num = 42;
num.toString(); // Returns '42’
Operators
- Addition of numbers
- Concatenation of strings
- Subtraction
- Multiplication
- Division
- Modulus
- Increment
- Decrement
- Exponentiation
Assignment Operators
= a = b a = b
+= a += b a = (a + b)
- = a -= b a = (a - b)
- = a *= b a = (a * b)
/= a /= b a = (a / b)
%= a %= b a = (a % b)
- *= a **= b a = (a ** b)
Comparison Operators
- Comparison operators are used to evaluate conditions by comparing two values.
- The
===and!==operators ensure strict equality by checking both value and data type, while relational operators like>,<,>=, and<=compare numerical values. -
Returns true if the first operand is greater.
- < Returns true if the first operand is smaller.
-
= Returns true if the first operand is greater or equal.
- <= Returns true if the first operand is smaller or equal.
- Used frequently in loops and conditional statements.
Ternary Operator
- The ternary operator
(?:)is a shorthand way to evaluate a condition that involves three parts:condition ? expression_if_true : expression_if_false
Summary
- JavaScript code can be included in an HTML document directly with or from an external file using
<script> </script>tags. - JavaScript can display output in an HTML element in an alert dialog box or in the browser’s console window.
- JavaScript statements may contain keywords, operators, values, and expressions.
- The JavaScript interpreter ignores tabs and spaces.
- JavaScript statements can be grouped in
{}curly bracket function blocks that can be called to execute when required. - Variable and function names may comprise letters, numbers, and underscore characters, but must avoid keywords.
- JavaScript variables may contain data types of String, Number, Boolean, Object, Function, Symbol, null, and undefined.
- Variables declared with the
letkeyword can be reassigned new values, theconstkeyword does not allow this change. - A function expression has statements grouped in
{}curly brackets for execution, and it returns a final single value. - The
()parentheses of a function expression may contain parameters for argument values to be passed from the caller. - A function block can include a
returnstatement to specify data to be passed back to the caller. - The JavaScript
()parentheses operator calls the function. - Hoisting allows function calls to appear in the script before the function declaration.
- Anonymous function expressions have no function name.
- Lexical scope is the environment in which the variable was created and can be global, local, or closure.
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