How can I declare value/s on Variable?

Question

How can I declare value/s on Variable using "Input" on Javascript.

HTML ( <input type="text" id="ofcourse" />
<button onclick="()">Submit</b> once clicked the variable has its value i guess )

JAVASCRIPT (
Function () {
VAR = " ";
}
)

LIKE THIS.... It's like making a database, using only Javascript and html. Is it possible?