> For the complete documentation index, see [llms.txt](https://akoserwal.gitbook.io/how-it-feels-to-learn-javascript/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://akoserwal.gitbook.io/how-it-feels-to-learn-javascript/js-eco-system/basic-concepts.md).
# Basic Concepts
## Understanding the Basic
Let's begin with understanding basic concepts of JavaScript.
**Variables:** number, string, boolean, null, undefined, objects.
To define a variable of any type use keyword.
> `var nameOfVariable = (assignment operator) Value ;`
>
> `(; is must. Chrome, Firefox understand your emotions & ignores bad habit missing ; for testing purpose)`
This is different from strongly-typed programming languages liked C, C++ or Java. Where the type-checking at compile time as opposed to dynamically typed languages (run-time checking) like JavaScript as shown in the above figure using Chrome V8 run-time. I would highly recommend to try this examples in your browser console.
> `var a = 5;`
>
> `<- undefined; (return type)`
Value return by run-time is of type `undefined.`While in-case of using operator `typeof(argument)`returns string `"number".`Declaration of a variable does not return any value that is why it returned with type `undefined.`Evaluated variable does not have a assigned value or defined return type; then it will return `undefined`*.*
You can override the value with any type of variable type. This seems bit odd and sounds type unsafe while working with a large code base. Using`var`keyword again would define a new variable in the memory space. Browser gives the intellisense about available properties and methods as shown in the figure.
