JSFiddle - React, Tailwind, and code Playground

HTML

<form>
        Enter number of rows: <input type="text" name="t1" /> <input
            type="button" value="Display Diomond"
            onclick="return myFunction(this.form)" />
    </form>

<p id="p"></p>

JavaScript

function myFunction(form) {
    var no;
    no = form.t1.value;
    no = no / 2;
    var no2 = no;
    var no3 = no;
    var no4 = no;
    var no5 = no;
    var no6 = no;
    var diamond = "";
    for ( var i = 0; i < no; i++) {
        for ( var index = 0; index < no2; index++) {
            diamond +="&nbsp&nbsp";
        }
        no2 = no2 - 1;

        for ( var index2 = 0; index2 < (i * 2) + 1; index2++) {
            diamond += "*";
        }
        diamond+="</br>";
    }
    diamond+="&nbsp&nbsp";
    for ( var i = 0; i < no3 + 1; i++) {

        for ( var index = 0; index <= i; index++) {
            diamond += "&nbsp&nbsp";
        }
        for ( var index2 = 0; index2 < (no4 * 2) - 3; index2++) {
            diamond += "*";
        }
        no4 = no4 - 1;
        diamond  += "</br>&nbsp";
    }
    document.getElementById("p").innerHTML = diamond;
}