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#JavaScript Data Types and String Methods

• Understand the core data types used in Javascript
• Use String Methods
• Access String Properties

When you initialize (or create) a variable, you have reserved some space in memory. Based on the kind -or type - of data, the interpreter will allocate a set amount of memory for your variable. Data types include strings, numbers, booleans, and "undefined". You'll learn more about these below.

Javascript is dynamically typed - or loosely typed - which means one variable can be reassigned to a different datatype.

JavaScript has a relatively small number of data types compared to other languages like Python. You've explored two of these data types already - numbers and strings.

1. Number: 1, 3.14, 0.13, -100, …
2. String (as in, a string of characters). examples include: "hi!", '-Cubs-', "1999" - note you can use either single or double quotation marks
3. Boolean: Represents either true or false
4. Undefined: has not been assigned a value, so the value is unknown
5. Null: This is a special keyword that means one of two things: no value or empty. The difference between null and undefined is that when a variable is null, it is still defined.

With numbers, you can use math operations (which we've seen before). With strings, there are string operations called methods.

A method is a function - a set of actions - attached to a piece of data. When a method is called on a string, it modifies that string based on that set of actions.

JavaScript has a number of built in methods that we can call on strings. The syntax for calling methods is dot notation, which looks like this:

variable.method()

Notice that all methods have a set of parentheses, where you can include arguments - additional information that describes how you want the method to be performed.

Open up the JavaScript console to test and play with the methods we discuss below. The following examples uses a variable, myText:

myText= "Code Ninja"

Feel free to create your own!

.charAt(x) - Returns the character at the “x” position within the string. Like many languages, Javascript starts counting at 0.

> myText.charAt(0)
< "C"

> myText.charAt(3)
< "e"

.concat(string1, string2) - Combines one or more strings (arguments) into the existing one.

> myText.concat(" at CSSI")
< "Code Ninja at CSSI"

Notice the space at the start of " at CSSI" - without it, our return value would be "Code Ninjaat CSSI"

A string represents a group of characters in a certain order. To find out which character is in a certain position, we can use indexing. Indexing is similar to counting, expect in Javascript, the index starts at 0. So in the string "Google", the capital G has an index of 0. The final e has an index of 5.

indexOf(substr, [start]) - Searches and (if found) returns the index number of the first match to the characters. If not found, -1 is returned.

> myText.indexOf("z")
< -1
> myText.indexOf("Ni")
< 5

substr(start, [length]) - Stands for substring - a string within a string. Returns the characters in a string beginning at “start” and through the specified number of characters, “length”. If length is not included, this function returns the remaining characters.

> myText.substr(1,6)
< "ode Ni"

###Different Method Syntaxes Sometimes, there are multiple syntaxes that do the same thing.

> "one ".concat("two")
"one two"
>"one " + "two"
"one two"

When we add strings to each other, we stick one right on the end of the other. This is called concatenation, and we can do it with the .concat() method or with the '+'.

You can make a new variable from the result of a function call.

> var extraAnger = "loathe".toUpperCase()
> extraAnger
< "LOATHE"

Method chaining is a powerful way to use methods - you can add them together to take multiple actions at once. What is happening is that you are calling a method on the result of another method:

>extraAnger.substr(0,2).toLowerCase().concat("ve")
<"love"

In the example above, we changed "LOATHE" (stored in extraAnger) to "love", by taking the substring of the first two characters ("LO"), lowercasing them ("lo"), and then concatenating "ve" to the end of the string ("love")!

Here's another example:

> var myPet = "hamster"
> mypet.toUpperCase().substr(0,3).concat(" SANDWICH")
< "HAM SANDWICH"

See if you can talk through what we just did here...

You can combine these tricks. You can even store the resultant value in the same variable you started with!

> var emotion1 = "angry"
> var emotion2 = "hungry"
> emotion1 = emotion2.substr(0,1) + emotion1 + "!!!"
> emotion1
< "hangry!!!"

You can also use dot notation to call a property of a variable to find out some valuable information about it. Unlike methods which act upon an object, properties just give us information about the object. Strings only have three properties, the most useful being the length property.

var emotion3 = "satiated"
> emotion3.length
< 8

var anotherEmotion = "bored"
> anotherEmotion.length
< 5

Since length is a property rather than a method, its notation does not include parenthesis () at the end.

##Resources W3 Schools String Methods

15 JavaScript String Functions