JSFiddle - React, Tailwind, and code Playground

HTML

<pre>
This is line 1<br>
    This is line 2<br>
    This is line 3<br>
    This is line 4<span id="marker">j</span><br>
    This is line 5<br>
    This is line 6<br>
    ...
<pre>

JavaScript

var text = document.getElementById('marker').previousSibling
console.log(text.wholeText.trim());