Data Types and Arrays
Data Types and Arrays
Most programming languages have a concept of data types. These are various kinds of data and are usually handled differently.
Consider, for example, the values 1 and “Hello, world!”. These are two different types of data and JavaScript understands them in separate ways.
Different Types of Numbers
JavaScript also understands different types of numbers. They can be integers or decimals. In JavaScript, these are all Numbers and can be used in calculations.
Letters and Numbers as Strings
Many programming languages, like JavaScript, understand letters, numbers, and other entries within single or double-quotations as strings.
In JavaScript, a String is a special data type that comes with some built-in abilities. They are understood as one unit and are changed using special JavaScript functionality.
They are often useful when some task needs to use text instead of numerical values. A common example might be to store the name of a user along with their identification as something like a number. Here's a real example (although in the related format of JSON) from actual Twitter data:
You can see that there are both numeric values (id) and string values ("William Shatner"), and that 15227791 appears as both data types.
Arrays as a Sequence of Values
JavaScript uses a third common type of data called an array. While not a number or collection of letters and numbers within quotations, an array can be thought of a sequence of values. The type of these values does not matter. In JavaScript, an array is simply a series of values separated by commas.
Arrays can also be inside other arrays. In these cases, the array is said to be multidimensional. Instead of being a sequence of values, a single dimension, it can have its own arrays that allow it have extra dimensions.
Arrays are called sequences of values because their position can be referenced. Much like a book, an entry in an array has an index. This is the position of the entry and, when used, its value is returned.
In most programming languages, arrays start with 0th position. To get the first (0) value in the array, it can be used with the reference using brackets. For example, using “[0]” would return the first value. Using “[3]” would return the fourth entry.
Why are arrays important?
Arrays are used in a variety of ways across programming environments. One of the most common usage is for positions. A multi-dimension array is a very common way to store X and Y coordinates (position[X][Y]) for displaying something on a screen, for example.
Another common usage is to group items together for storage or organizational purposes. All of the students within a class might be kept in an array. When programming a game in JavaScript, all of the enemies in a level might also be kept in an array.
Play with the Code (Repl.it):
Take a moment to play with the code and concepts in the embedded Repl.it viewer below.
Try changing what's in the array and which value, from which array, you want to display.