how to enable and disable Button

--------HTML--------- 

<div id="butt1">
    <button id="btn11" onclick="check(this);">check1</button>


</div>

<div id="butt2">
    <button id="btn21" onclick="check23(this);" disabled hidden>check2</button>

</div>

----------java script-------

<script>


    var btnval = true;


    function check23(btnval) {

        document.getElementById("show2").innerHTML = "check 2: disable";
        document.getElementById("btn2").disabled = this.btnval;
        document.getElementById("btn2").hidden = this.btnval;
        document.getElementById("show4").innerText = "check 1:  enabel";
        document.getElementById("btn1").disabled = !this.btnval;
        document.getElementById("btn1").hidden = !this.btnval;

    }
    function check(btnval) {

            document.getElementById("show2").innerHTML = "check 2: enable";
            document.getElementById("btn2").disabled = !this.btnval;
        document.getElementById("btn2").hidden = !this.btnval;
            document.getElementById("show4").innerText = "check 1: disable";
            document.getElementById("btn1").disabled = this.btnval;
        document.getElementById("btn1").hidden = this.btnval;


    }
</script>