are variables and objects accessible in all javascripts files in the same project?

im not grasping how two javascript files are linked? example:

script1.js ----

var students = [ { name: 'Dave', track: 'Front End Development', achievements: 158, points: 14730 } ];

scripts2.js--------

var message = ''; var student; for (var i = 0; i < students.length; i += 1) { student = students[i]; message += '<h2>Student: ' + student.name + '</h2>'; message += '<p>Track: ' + student.track + '</p>'; message += '<p>Points: ' + student.points + '</p>'; message += '<p>Achievements: ' + student.achievements + '</p>';

QUESTION: how does scripts2.js even know the variable students exist as an array of objects in a seperate file? sure they are both linked to the html file but not to each other?

i just can't under why i can create

var test = 0;

in scripts1.js

then change the value

test = 1;

in scripts2.js

its great to be able to, but i just want to know how and why!

thanks