Javascript Basic Increment and Decrement

Question

Why isn't dec() decreasing the value?

<div id="variableTest">8</div>
<label id="incButton" onclick="inc()">+</div> </br>   
<label id="decButton" onclick="dec()">-</div> </br>
    ​

function dec() {
    var testDec = document.getElementById("variableTest").innerHTML;
    testDec--;
}

function inc() {
    var testInc = document.getElementById("variableTest").innerHTML;
    testInc++;
}​

http://jsfiddle.net/fv6VA/8/

Answer 1

element.innerHTML returns a string, not a number. You should use something like this:

var element = document.getElementById("variableTest");
element_number = parseFloat(element.innerHTML);
element_number++;
element.innerHTML = element_number;

Answer 2

Essentially you have made a copy of innerHTML, and are just decrementing it in javascript memory. You haven't actually set the innerHTML of the variableTest node.

function dec() {
    var testDec = document.getElementById("variableTest").innerHTML;
    testDec--;
    document.getElementById("variableTest").innerHTML = testDec;
}

UPDATE

Also, your HTML is messed up. You need to close your label properly

<div id="variableTest">8</div>
<label id="incButton" onclick="inc()">+</label> </br>   
<label id="decButton" onclick="dec()">-</label> </br>

Answer 3

<div class="container">
<input type="button" onclick="decrementValue()" value="-" />
<input type="text" name="quantity" value="1" maxlength="2" max="10" size="1" id="number" />
<input type="button" onclick="incrementValue()" value="+" />
</div>

<script type="text/javascript">
function incrementValue()
{
    var value = parseInt(document.getElementById('number').value, 10);
    value = isNaN(value) ? 0 : value;
    if(value<10){
        value++;
            document.getElementById('number').value = value;
    }
}
function decrementValue()
{
    var value = parseInt(document.getElementById('number').value, 10);
    value = isNaN(value) ? 0 : value;
    if(value>1){
        value--;
            document.getElementById('number').value = value;
    }

}
</script>