Question

I have the form below. Using the buttons, the value in the text field should be increase or decreased. the decrease button works fine, but the increase button simply appends a ’10’ to the end of the number, so 100 will become 10010, rather than 110. Can someone let me know how to fix this?

<form name="hello" id="hello">
<table border=0>
<tr>
<td width=200>
<input type=text id="input" style="height: 30px; width: 200px" name=amount value=5>
</td>
<td>
<table border=0>
<tr height=12><td width=20>
<input type=button value="+" style="height: 15px; width: 25px; text-align:center; vertical-align:center; font-size:8px;" onClick="javascript:this.form.amount.value+=10;">
</td></tr>
<tr height=12><td width=20>
<input type=button value="-" style="height: 15px; width: 25px; text-align:center; vertical-align:center; font-size:8px;" onClick="javascript:this.form.amount.value-=10;">
</td></tr>
</table>
</td>
</tr>
</table>
</form>

Answer 1

Your javascript is treating it like a string concatenation. Parse the value into an int, do the math, and then set the value.

The onClick for your + button

onClick="javascript: this.form.amount.value = parseInt(this.form.amount.value, 10) + 10;"