JSFiddle - React, Tailwind, and code Playground

JavaScript

var a = 'John';
window.b = 'Jane';
c = 'Jack';

alert(a); // John
alert(b); // Jane
alert(c); // Jack

alert(window.a); // John
alert(window.b); // Jane
alert(window.c); // Jack

alert(delete a); // false
alert(delete b); // true
alert(delete c); // true

alert(a); // John
try { alert(b); } catch (e) { alert(e); } // throws ReferenceError: b is not defined
try { alert(c); } catch (e) { alert(e); } // throws ReferenceError: c is not defined

window.b = 'Jane';
c = 'Jack';

alert(delete window.a); // false
alert(delete window.b); // true
alert(delete window.c); // true

alert(window.a); // John
alert(window.b); // undefined
alert(window.c); // undefined

alert(a); // John
try { alert(b); } catch (e) { alert(e); } // throws ReferenceError: b is not defined
try { alert(c); } catch (e) { alert(e); } // throws ReferenceError: c is not def