编写脚本以在提交之前将复选框值连接到字符串中

我似乎让它完全按照需要工作。但还是忍不住觉得JS需要整理一下！似乎很期待我怀疑应该是一段较小的代码。。。就像我说的：我的JS差到根本不存在！

<script type="text/javascript">
	function checkTotal() {
        document.ppform.os1.value = '';
        if (document.getElementById('os10').checked){
            var cb1str = document.ppform.cb1.value;
        } else {
            var cb1str = '';
        }
        if (document.getElementById('os11').checked){
            var cb2str = document.ppform.cb2.value;
        } else {
            var cb2str = '';
        }
        if (document.getElementById('os12').checked){
            var cb3str = document.ppform.cb3.value;
        } else {
            var cb3str = '';
        }
        if (document.getElementById('os13').checked){
            var cb4str = document.ppform.cb4.value;
        } else {
            var cb4str = '';
        }
        if (document.getElementById('os14').checked){
            var cb5str = document.ppform.cb5.value;
        } else {
            var cb5str = '';
        }
        if (document.getElementById('os15').checked){
            var cb6str = document.ppform.cb6.value;
        } else {
            var cb6str = '';
        }
        if (document.getElementById('os16').checked){
            var cb7str = document.ppform.cb7.value;
        } else {
            var cb7str = '';
        }
		var sum = cb1str.concat(cb2str).concat(cb3str).concat(cb4str).concat(cb5str).concat(cb6str).concat(cb7str);
		document.ppform.os1.value = sum;
	}
</script>

<div id="buyform">
            <form target="paypal" id="ppform" name="ppform" action="https://www.paypal.com/cgi-bin/webscr" method="post" >
            <input type="hidden" name="cmd" value="_cart">
            <input type="hidden" name="business" value="myPPbusinessid">
            <input type="hidden" name="lc" value="GB">
            <input type="hidden" name="item_name" value="Form Title">
            <input type="hidden" name="button_subtype" value="products">
            <input type="hidden" name="no_note" value="0">
            <input type="hidden" name="no_shipping" value="2">
            <input type="hidden" name="currency_code" value="GBP">
            <input type="hidden" name="add" value="1">
            <input type="hidden" name="bn" value="PP-ShopCartBF:btn_cart_LG.gif:NonHosted">
            <div><input type="hidden" name="on0" value="Options"><h5>Options</h5></div>
            <div>
                <select name="os0" id="os0" required>
            		<option value="Chosen Product">Any quantity £10.00 GBP</option>
            	</select>
            </div>
            <input type="hidden" name="on1" value="Colours">
            <div>
            <input type="checkbox" name="cb1" value="Red " id="os10" onchange="checkTotal()" /><label for="os10"></label>
            <input type="checkbox" name="cb2" value="Green " id="os11" onchange="checkTotal()" /><label for="os11"></label>
            <input type="checkbox" name="cb3" value="Orange " id="os12" onchange="checkTotal()" /><label for="os12"></label>
            <input type="checkbox" name="cb4" value="Purple " id="os13" onchange="checkTotal()" /><label for="os13"></label>
            <input type="checkbox" name="cb5" value="Yellow " id="os14" onchange="checkTotal()" /><label for="os14"></label>
            <input type="checkbox" name="cb6" value="Black " id="os15" onchange="checkTotal()" /><label for="os15"></label>
            <input type="checkbox" name="cb7" value="Blue " id="os16" onchange="checkTotal()" /><label for="os16"></label>
            <input type="hidden" name="os1" value="">
            </div>
            <input type="hidden" name="currency_code" value="GBP">
            <input type="hidden" name="option_select0" value="Options">
            <input type="hidden" name="option_amount0" value="10.00">
            <input type="hidden" name="option_index" value="0">
            <input type="hidden" name="currency_code" value="GBP">
            <input type="submit" border="0" name="submit" id="submit" value="Purchase" class="buynow mb0"></form>
            </div>