Advanced Web Programming - Chapter 9: Arrays

Advanced Web Programming - Chapter 9: Arrays, Numbers

• Arrays: Used to handle lists of data.
• Common tasks performed using array properties are discussed.
• Numerical values and the Math object are covered.

Arrays

• An array is a list of items, conceptually like a numbered list.
• The items in an array are called elements or array values.
• The order of elements is significant; they are indexed (starting from 0).
• Example:
  • Grocery list: ["Milk", "Eggs", "Frosted Flakes", "Salami", "Juice"]

Creating an Array

• To create an array (empty): var groceries = [];
• To create an array with values: var groceries = ["Milk", "Eggs", "Frosted Flakes", "Salami", "Juice"];
• Values are separated by commas.

Accessing Array Values

• To access an item, use its index number inside square brackets: groceries[1] (accesses the second item).
• Index values start from zero.
• Use array.length to get the number of items in an array.

Adding Items to an Array

• push(): Adds items to the end of an array. Example: groceries.push("Cookies");
• unshift(): Adds items to the beginning of an array. Example: groceries.unshift("Bananas");
• Both methods return the new array length.

Removing Items from an Array

• pop(): Removes and returns the last item.
• shift(): Removes and returns the first item.

Removing Items from an Array (Cont.)

• slice(): Copies a portion of an array to a new array. Example: var newArray = groceries.slice(1. 4); This copies elements from index 1 up to, but not including, index 4.

Finding Items in an Array

• indexOf(): Returns the index of the first occurrence of an item. Example: groceries.indexOf("Eggs");
• lastIndexOf(): Returns the index of the last occurrence of an item.

Merging Arrays

• concat(): Merges two or more arrays into a new array. Example: var goodAndBad = good.concat(bad); good and bad are the two arrays.

Numbers (Using Numbers)

• var stooges = 3; - A simple number variable.
• pi = 3.14159; - A complex number example.

Operators (Doing Simple Math)

• Basic arithmetic operators: +, -, *, /, %.
• total = 4 + 26; adds two values together.
• average = total / 2; divides values

Incrementing and Decrementing

• i++: Increments i by 1.
• i--: Decrements i by 1.
• i += n: Increments i by n.
• i -= n: Decrements i by n.

Special Values (Infinity and NaN)

• Infinity: Represents a very large number.
• NaN: Represents "Not a Number" (results of invalid operations)

The Math Object

• Provides mathematical functions and constants (like Math.PI).
• Used to perform more complex calculations and operations.

Trigonometric Functions

• Math.sin(), Math.cos(), Math.tan(), etc., to perform trigonometric calculations

Powers and Square Roots

• Math.pow(): Raises a number to a power (e.g., Math.pow(2, 4) ).
• Math.exp(): Raises Euler's constant (e) to a power.
• Math.sqrt(): Calculates the square root.

Absolute Value

• Math.abs(): Returns the absolute value of a number. Example: Math.abs(-5) returns 5.

Random Numbers

• Math.random(): Generates a random number between 0 (inclusive) and 1 (exclusive).

Lab

• Links to online resources for further practice (w3schools examples).