Question

我试图从组合框中获取“值”，并简单地向其中添加一个。我认为我需要将其转换为整数，但也无法使解析工作。接下来，我想把这个新数字放进一个文本框里。

<script type="text/javascript">
    function GetNextCategoryNum(sel)
    {
        var NextNumber; 
        var number = sel.options[sel.selectedIndex].value; 
        NextNumber = number ++1;
        alert("Last number used "  + number );
        textbox = NextNumber 
    }
</script>

Answer 1

Three mistakes in your code:
1. value will return a string. So you need to change it to an integer.
2. "number ++1" is wierd. What you need is ++number. If you do not want to increase "number" but "NextNumber", then just put on number + 1.
3. What is "textbox"? if it refers to a textbox object then you need declaring it.

所以我的建议是：

<script type="text/javascript">
    function GetNextCategoryNum(sel)
    {
        var NextNumber; 
        var textbox = document.getElementById("textbox");
        var number = parseInt(sel.options[sel.selectedIndex].value); 
        NextNumber = number + 1;
        alert("Last number used "  + number );
        textbox.value = NextNumber;
    }
</script>

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