Part 1: Javascript Types

In this lecture we're going to talk about JavaScript built-in types. Now, first of all, what is a type? A type is a particular data structure. Now each language defines some built in types, and JavaScript is no different. Built in types, can be used to build other data structures, that you can then use for your particular business logic. Now JavaScript has seven built-in types, six primitive, and one object type. So what is an object in JavaScript? Well in JavaScript an object is nothing more than a collection of name/value pairs. You can have one name value pair, or it can have zero name value pairs. But it is a collection of name value pairs. Let's take a look at one a quick example might look like, visually. 

So, here I have a person object and it has a bunch of different name value pairs. First name, Yaakov, last name Chaikin, social and so on. So first name would be the name and Yaakov would be the value and so too a value doesn't necessarily have to be a single value, it could be a nested object. So a name here, for example is social, the name of the property of the object. And the value of that property, is an entire other object, that has again, name value pairs. So that's object type. What about primitives? Well primitive type is a type that represents a single, immutable value. So what do that mean? A single value means it's not an object, remember an object is collections of name, value pairs, even simplest object there is there is a name of value pair. Well the very simplest one has zero name value pairs. But the very simplest one that has some data in it is a name value pair. It's not a single value. What does immutable mean? Immutable means once it's set, once that value is set It cannot be changed. It means that once you set it, the value of the variable becomes read-only. You could certainly create another value based on an a existing value but the memory space that was allocated for the first value is not changed. Instead, you create a new memory space for the new value. So let me run down one by one of all the primitive types that JavaScript defines. First of all, boolean. Well boolean can only have two values, either true or false. And true and false are reserved keywords in JavaScript language. Now if you've ever done any programming at all and this course assumes that you have. You should be very familiar with this type. Enough said, really. Another type is called undefined. The undefined data type signifies that no value has ever been set on this particular variable of this type. This is the value that every variable gets when the JavaScript engine sets up the variable in memory when it defined but has never been assigned any value yet. 

And it can only have one value. And it's a reserved keyword undefined. Now you can set a variable to the keyword undefined yourself manually, but you should never ever do that. And the reason is, is because it's meaning is that it's never been defined. So defining it and then setting it to undefined Is really counter to its core meaning. If you ignore this advice and explicitly in your code, set a variable to the value of undefined, that will create tremendous confusion in your code. And confusion and code is never a good thing. Another value that the JavaScript language defines is null. Null signifies the lack of value. Now, the lack of value as opposed to undefined which signifies the lack of definition. There's only one value that could ever set for that type and that value is the reserved keyword, null. And it's also perfectly normal and perfectly okay to explicitly in your code set a variable to the null value. 

Another type is number. Well number is actually the only numeric type in JavaScript and it's always represented under the hood as a double-precision 64-bit floating point. In other words, JavaScript does not have integer type. Integers in JavaScript are just a subset of doubles instead of a separate data type. Another data type is strings and string in JavaScript is very similar to the string type in other languages in that it is a sequence of characters used to represent text and you can define strings either using single or double quotes, either one is 100% legal. 

The last primitive type that I'll mention, is symbol. Now we're not really going to cover this data type in this class. And the reason is, is that it's new to the ES6, otherwise known as ecmoscript 6. Now ecmoscript 6, was released in 2015, around mid 2015, and it just isn't widely supported. Were really used yet. It will probably become quite popular in the next number of years, but it's not there yet, so were going to skip it for this course. Okay, so time to go to the code editor and see some examples.

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