JSFiddle - React, Tailwind, and code Playground

HTML

<span>The quick brown fox jumps over the lazy dog</span>

CoffeeScript

$(document).ready ->
  container = $('span')
  container.click (e) ->
    container_width = container.width()
    char_width = p_width / container.text().length
    position_inside = e.pageX - container.offset().left
    console.log("#{ Math.floor(position_inside / char_width) - 1 }")