JSFiddle - React, Tailwind, and code Playground

HTML

<textarea id="quote" readonly> 
sample text that can be copied into another textarea
</textarea>

<textarea contenteditable="false" id="output" name="selected"></textarea> 

<div id="output2">

</div>

JavaScript

var quotearea = document.getElementById('quote')
var output = document.getElementById('output')
quotearea.addEventListener('mouseup', function(){
    if (this.selectionStart != this.selectionEnd){ // check the user has selected some text inside field
        var selectedtext = this.value.substring(this.selectionStart, this.selectionEnd)
        output.innerHTML = selectedtext
    }
}, false)