Functions in Programming

Functions in JavaScript

• A function is a block of code designed to perform a particular task and can be executed by an event or by a call to the function.
• A JavaScript function is defined with the function keyword, followed by a name, and then parentheses ().
• Function names can contain letters, digits, underscores, and dollar signs (same rules as variables).

Function Syntax

• function functionName(parameter1, parameter2, …) { code to be executed }

Return Statement

• Functions that return a value must use the return statement.
• Example: function product(a, b) { return a * b; }

Conditional Statements

• if statement: executes code if a specified condition is true.
• if...else statement: executes code if the condition is true and another code if the condition is false.
• if...else if....else statement: selects one of many blocks of code to be executed.
• switch statement: selects one of many blocks of code to be executed.

Conditional Statement Syntax

• if (condition) { code to be executed if condition is true }

Example of if Statement

• if (time < 12) { write a "Good morning" greeting }

Adding Strings and Numbers

• When you add a number and a string, the result will be a string.

Examples of Adding Strings and Numbers

• var x = 5 + 5;
• document.write(x + "");
• x = "5" + "5";
• document.write(x + "");
• x = 5 + "5";
• document.write(x + "");
• x = "5" + 5;
• document.write(x + "");

Comparison Operators

• Used in logical statements to determine equality or difference between variables or values.

Logical Operators

• Used to combine conditions in logical statements.

Conditional Operator

• Assigns a value to a variable based on some condition.
• Syntax: variablename = (condition) ? value1 : value2;

Variables in JavaScript

• Variable names are case sensitive.
• Variable names must begin with a letter, an underscore (_), or a dollar sign ($).
• Subsequent characters can be letters, digits, underscores, or dollar signs.

Local and Global Variables

• Local variables: declared within a JavaScript function and can only be accessed within that function.
• Global variables: declared outside a function and can be accessed by all scripts and functions on the web page.

Example of Local and Global Variables

• function displaymessage() { var x = 3; alert("Local x = " + x + " , Global y=" + y); }
• var y = 5; alert(" Global y = " + y);

Arithmetic Operators

• Used for arithmetic operations such as addition, subtraction, multiplication, division, etc.

Assignment Operators

• Used to assign values to JavaScript variables.

The + Operator

• Can be used to add string variables or text values together.
• Example: txt1 = "What a very"; txt2 = "nice day"; txt3 = txt1 + txt2; txt4 = txt1 + " " + txt2;