JSFiddle - React, Tailwind, and code Playground

HTML

<p>Input:</p>
<pre id=in>a1b2c3d4,,,a9b10c11d12</pre>
<p>Output:</p>
<pre id=out>?</pre>

CSS

pre { font-size: x-small }

JavaScript

var input = $('#in').text();
var inp = input.split(','),
    out = [], i, j, m, p, output;
for (i = 0; i < inp.length; i++) {
    if (inp[i]) {
        out[i] = {};
        m = inp[i].match(/[a-z]+\d+/ig);
        for (j = 0; j < m.length; j++) {
            p = /([a-z]+)(\d+)/i.exec(m[j]);
            out[i][p[1]] = p[2];
        }
    }
}
output = JSON.stringify(out);
$('#out').text(output);