html, body { margin: 0; }

body { font-family: sans-serif; border-top: 5px solid #0074C1; }

form { margin: 10px; }

label { cursor: pointer; }

<form onsubmit="convert(this); return false">

<h1>Hexadecimal float to decimal float converter</h1>

<p>

<label for="f64"><input id="f64" name="precision" value="f64" type="radio" checked /> f64</label>

<label for="f32"><input id="f32" name="precision" value="f32" type="radio" /> f32</label>

<input id="pre" type="text" value="test(" />

<input id="post" type="text" value=");" />

<button>Convert</button>

</p>

<p><textarea cols="120" rows="20" id="input"></textarea></p>

<p><textarea cols="120" rows="20" id="output" readonly></textarea></p>

<script src="hexfloat.js"></script>

function convert(form) {

let isF64 = document.getElementById("f64").checked;

let pre = document.getElementById("pre").value;

let post = document.getElementById("post").value;

let input = document.getElementById("input").value;

document.getElementById("output").value = input

.replace(/\b(\-?0x[0-9a-fA-F]*(?:\.[0-9a-fA-F]+)?[pP][+-]?[0-9]+\b)/g, ($0, $1) => {

let val = parse($1);

return val.toPrecision(isF64 ? 18 : 10);

})

.replace(/(\d\.[0-9])0+\b/g, "$1")

.replace(/\bnan\b/g, "NaN")

.replace(/\binf\b/g, "Infinity")

.replace(/^T\(R\w, */mg, pre)

.replace(/\);?$/mg, post)

.replace(/ +/g, " ");