How to retrieve List page field value for use in JavaScript code.

Good day all.

I have a piece of java script for which I would like to input

a field value displayed on the list page. How do I grab

the field value to use in the JS code? Also, am I right in assuming

that the JS code should be placed in the JavaScript OnLoad event page?

Thanks in advance for your assistance.
/JavaScript/JQuery/
var amount = ?,

height = amount * 80/100 + 20;
$('.lq').css({height : height + '%'});