reading-notes

Class 7 Notes - Programming with JavaScript

Useful JS Commands

command: use strict

• tells JavaScript to perform based on strict JS rules

command: .toLowerCase()

• converts users input to ONLY lowercase

command: .toUpperCase()

• converts users input to ONLY uppercase

Control Flow

The control flow is the order in which a computer executes/runs statements in a script.

Code is typically executed/ran from the first line in a file down to the last line. Exceptions to this rule are infrequent but include structures that change the control flow such as conditionals and loops.

An example of this exception can occur when a user is entering data on a webpage form. If a user attempts to submit data, but has left a required field empty (usually denoted by an asterisk), then the script will stop and prompt the user to fill in the missing information. A conditional structure or if...else statement is used in this case so that different code is executed depending on whether necessary information has been completed or not.

Example: if (isEmpty(field)) { promptUser(); } else { submitForm(); }

A typical script in JavaScript or PHP (Hypertext Preprocessor) includes many control structures including conditionals, loops, and functions.

JavaScript Functions

A function is a block of code which performs/executes a specific task. A JS function is executed when it is invoked or called.

Function Syntax

A JS function is defined with the function keyword followed by a name or unique identifier and then parentheses (). Similar to variable names, function names can contain letters, digits, underscores, and dollar signs. Parentheses can include multiple parameters separated by commas: (parameter1, parameter2). The code that will be executed by the function is then placed inside curly brackets {}.

Function Invocation

Code inside the function will execute when something invokes or “calls” the function. Functions are invoked when:

• An event occurs, e.g. a button click
• It is invoked (called) from the JavaScript code
• Automatically (self-invoked)

The () operator invokes the function in a set of code. For example, myFunction is the function object and myFunction() is the function result.

Function Return

When JS receives a return statement, the function will stop executing. Functions usually compute a return value which is “returned” back to the “caller”.

Examples of Function Structure

function uniqueName(parameters){code to be executed}

function addTwoNumbers(number1, number2){return number1 + number2}

console.log(number1 + number2);}

addTwoNumbers(5, 3); OR addTwoNumbers(“Hello “, “world”);

Why are Functions Used?

Functions allow for code to be re-used by defining it once and using it repeatedly throughout a script. The same code can also be used multiple times with different arguments to produce different results/outputs.

JavaScript Operators

Types of JavaScript Operators:

• Arithmetic Operators
• Assignment Operators
• Comparison Operators
• Logical Operators
• Conditional Operators
• Type Operators

Arithmetic Operators

Arithmetic operators are used to perform arithmetic on numbers:

Operator	Description
+	Addition
-	Subtraction
*	Multiplication
**	Exponentiation
/	Division
%	Modulus (Division Remainder)
++	Increment
–	Decrement

Assignment Operators

Operator	Example
=	x = y
+=	x = x + y
-=	x = x - y
*=	x = x * y
/=	x = x / y
%=	x = x % y
**=	x = x ** y

Comparison Operators

Operators	Description
==	equal to
===	equal value and equal type
!=	not equal
!==	not equal value or not equal type
>	greater than
<	less than
>=	greater than or equal to
<=	less than or equal to
?	ternary operator

Logical Operators

Operators	Description
&&	logical AND
II	logical OR
!	logical NOT

JS operator: && Logical AND

• true && true —> true
• false && true —> false
• true && false —> false
• false && false —> false

JS operator: || Logical OR

• Either side has to be true
• true || false —> true
• false || true —> true

Expressions and Operators

The above link is a detailed reference to JavaScript expressions and operators. An expression is a valid unit of code that resolves to a value.

Functions

The above link is a detailed reference to functions which are the basic building blocks in JavaScript. A function is a set of statements that perform/execute a task or calculate a value.