JSFiddle - React, Tailwind, and code Playground

HTML

<div id="log">
    If passed by reference, the arrays below will be exactly the same:<br />
</div>

CSS

samp {
    color: green;
}

JavaScript

var data = [];

function a( $log , d ) {
    d=[];
    d.push('foo');
    $log.append( "I'm <samp>d</samp> from <samp>a()</samp>: <samp>" + JSON.stringify(d) + "</samp><br />" );
}

data.push('bar');

var $log = $('#log');

a( $log , data);

$log.append(  "I'm <samp>data</samp> from outside: <samp>" + JSON.stringify(data) + "</samp><br />" );