How can I use a variable of one <script> in another <script> in javascript?

If the two script tags are on the same page, any variable declared outside of the scope of a function is global to the page.

Make it global;

script1.js

 var foobar = "O HAI";

script2.js

  alert(foobar);

If the two script tags are on the same page, any variable declared outside of the scope of a function is global to the page. However, it does matter which script is loaded first for some applications.

When you declared a variable inside a <script> , you can access it anywhere simply by using this:

var myValue= window.yourProperty;