#JavaScript (ES6) + HTML, 77 74 bytes
JavaScript (ES6) + HTML, 77 74 bytes
f=c=>setTimeout(f,250,-~c%4,o.value="Loading... "+"|/-\\"[~~c])
<input id=o
##Try It
Try It
(f=c=>setTimeout(f,250,-~c%4,o.value="Loading... "+"|/-\\"[~~c]))()
<input id=o>