Untitled

<!DOCTYPE html>
<html>
<body>

Checkbox1: <input type="checkbox" id="myCheck1">
Checkbox2: <input type="checkbox" id="myCheck2">
Checkbox3: <input type="checkbox" id="myCheck3">
Checkbox4: <input type="checkbox" id="myCheck4">
Checkbox5: <input type="checkbox" id="myCheck5">
Checkbox6: <input type="checkbox" id="myCheck6">
ALL: <input type="checkbox" id="myCheckAll" onchange="checkAll()">

<button onclick="check()">Check Checkbox</button>
<button onclick="uncheck()">Uncheck Checkbox</button>

<script>
function check() {
    document.getElementById("myCheck").checked = true;
}

function uncheck() {
    document.getElementById("myCheck").checked = false;
}
function checkAll() {
    if (!document.getElementById("myCheckAll").checked) {
    document.getElementById("myCheck1").checked = false;
    document.getElementById("myCheck2").checked = false;
    document.getElementById("myCheck3").checked = false;
    document.getElementById("myCheck4").checked = false;
    document.getElementById("myCheck5").checked = false;
    document.getElementById("myCheck6").checked = false;
    } else {
    document.getElementById("myCheck1").checked = true;
    document.getElementById("myCheck2").checked = true;
    document.getElementById("myCheck3").checked = true;
    document.getElementById("myCheck4").checked = true;
    document.getElementById("myCheck5").checked = true;
    document.getElementById("myCheck6").checked = true;
    }
}
</script>

</body>
</html>