Untitled

<!DOCTYPE html>
<html>
    <head>
        <title></title>
    </head>
    <body>
        <header>
            My Calculator
            <h1></h1>
        </header>
        <section>
            <article>
                <form name="calculate">

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

                    <br/>
                    <button style="height:40px;width:40px" id="clrBtn">C</button>
                    <button style="height:40px;width:40px" id="delBtn">del</button>
                    <button style="height:40px;width:40px" id="perBtn">%</button>
                    <button style="height:40px;width:40px" id="divBtn">/</button>
                    <br/>
                    <button style="height:40px;width:40px">7</button>
                    <button style="height:40px;width:40px">8</button>
                    <button style="height:40px;width:40px">9</button>
                    <button style="height:40px;width:40px" id="mulBtn">X</button>
                    <br/>
                    <button style="height:40px;width:40px">4</button>
                    <button style="height:40px;width:40px">5</button>
                    <button style="height:40px;width:40px">6</button>
                    <button style="height:40px;width:40px" id="subBtn">-</button>
                    <br/>
                    <button style="height:40px;width:40px">1</button>
                    <button style="height:40px;width:40px">2</button>
                    <button style="height:40px;width:40px">3</button>
                    <button style="height:40px;width:40px" id="addBtn">+</button>
                    <br/>
                    <button style="height:40px;width:84px">0</button>
                    <button style="height:40px;width:40px" id="decBtn">.</button>
                    <button style="height:40px;width:40px" id="eqlBtn">=</button>


                <script type ="text/javascript">

                    var myNum = 0;

                    document.getElementById("output").innerHTML = myNum;
                    document.getElementById("clrBtn").onclick = function() {buttonClick()};

                     function buttonClick() {
                        myNum = document.getElementById("clrBtn").innerHTML
                        document.getElementById("output").innerHTML = myNum;
                        console.log(myNum);
                    }

                </script>
            </article>
        </section>
        <footer>

        </footer>
    </body>
</html>