JSFiddle - React, Tailwind, and code Playground

HTML

<div id="input">
    <h1>Input</h1>
</div>
<div id="output">
    <h1>Becomes</h1>
</div>

JavaScript

// Take the following string
var string = "spanner, span, spaniel, span";
$('#input').append(string);

// Find the duplicates
// Remove the duplicate, leaving a single occurance of the word in place

// Output the following
var uniqueList=string.split(',').filter(function(allItems,i,a){
    return i==a.indexOf(allItems);
}).join(',');

$('#output').append(uniqueList);