JavaScript Strings and Arrays Kevin Harville

Strings and Arrays Strings are indexed groups of CHARACTERS. Arrays are indexed groups of numbers. Therefore we can refer to a particular number or letter by referring to its index.

Array Examples I could have an array of images: myImage[1] = “myDog.jpg” myImage[2] = “myCat.jpg” myImage[3] = “myFish.jpg” Or an array of the students’ scores: classScore[0] = 100 classScore[1] = 95 classScore[2] = 86

Strings and Arrays Strings and Arrays are objects rather than variables. Objects have properties and methods myString = “Kevin” makes it look like a variable, but is actually a shortcut to make strings easy to use. IMPORTANT: Strings and Arrays are indexed, or counted, starting at 0, not 1.

String Properties myString.length

String Methods String objects have several useful methods: myString.toLowerCase(); myString.toUpperCase(); Others Follow…

String Methods: Substring myString.substring(start, end+1); “Kevin”.substring(0,2) returns “Ke” “Kevin”.substring(1,3) returns “ev” REMEMBER: ARRAYS START AT ZERO!

String Methods: charAt charAt returns the value of the character at an index position: “Kevin”.charAt(4) returns “n” why “n”?

String Methods: indexOf “Kevin”.indexOf(“vi”) returns 2 indexOf returns –1 if it is not found: Kevin.indexOf(“Joe”) returns –1 You can specify the starting position: “Rin Tin Tin”. indexOf(“in”, 4) returns 5 To find multiple occurrences repeat the process.

String Methods: lastIndexOf Same as indexOf, but starts searching from the end.

String Methods: Split This method creates an array myNewStrings = “Quick Brown Fox”.Split(“ “); myNewStrings[0] = “Quick” myNewStrings[1] = “Brown” myNewStrings[2] = “Fox”

Some Other String Methods: .replace (4.0 Browsers or higher) HTML functionality, such as .fontcolor .fontsize .strike .etc.

Arrays Again, an array is a group of indexed values. For instance, instead of having individual class scores Score1, Score2, etc, you can have score[0], score[1]…score[30]. So, What’s the difference?

Arrays The difference is that the indexes can themselves be referred to by a variable! score[x] = 7 score[x + 1] = 4 score[y]= 9

Arrays When we want a group of related data, we may declare an Array object: myArray = new Array(50) This would set up 50 elements, from 0 to 49. There is no 50th element.

Arrays That indexing ability makes keeping track of related data very easy. Name[7] = “Fred” Lab1[7] = 5 Lab2[7] = 4 Midterm[7] = 12

Array Object: Sort Method Using the sort method, you can sort a numeric or alphabetic array. MyArray.sort()

Summary Strings and arrays are used in most scripts Learning them is necessary and a useful programming skill.