<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title></title>
    <style type="text/css">
        .btn
        {
            cursor: pointer;
            height: 25px;
            width: 80px;
            line-height: 23px;
            margin: 0px 4px;
            padding: 0 8px; *padding:02px;text-align:center;display:inline;border-radius:2px;font-size:12px;}</style>
</head>
<body>
    <h1>
        JavaScript自定义函数实现字符串SubString</h1>
    输入：<br />
    <input name="txt_Input" type="text" value="www.slowx.net" id="txt_Input" style="width:99%;" />
    <br />
    StartIndex：<br />
    <input name="txt_SubInput" type="text" value="3" id="txt_SubInput" style="width:99%;" />
    <br />
    <br />
    <input type="button" id="btn_OK" class="btn" value="确定" onclick="OkClick()" />
    <br />
    <br />
    输出：<br />
    <input name="txt_Output" type="text" id="txt_Output" style="width:99%;" /> </body>
</html>

function StrTrim(str) {
        // Trim + //
        if (str == null)
            return "";

return str.replace(/(^\s*)|(\s*$)/g, "");
    }

function MathToInt(str, defaultValue) {
        // 转Int数字 //
        var theStr = StrTrim(str);

if (theStr == "")
            return defaultValue;

if (theStr == "0")
            return 0;

var theResult = parseInt(theStr, 10);

if (theResult == NaN || theResult == undefined)
            return defaultValue;

return theResult;
    }

function StrSubString(str, startIndex) {
        if (str == null || str == "")
            return "";

if (startIndex == 0)
            return str;

var theLen = str.length;

if (startIndex >= theLen)
            return "";

return str.substr(startIndex, theLen);
    }

function OkClick() {
        var inputCtrl = document.getElementById("txt_Input");
        var subInputCtrl = document.getElementById("txt_SubInput");
        var outputCtrl = document.getElementById("txt_Output");

var theValue = inputCtrl.value;
        var theChar = subInputCtrl.value;

var startIndex = MathToInt(theChar, null);

if (startIndex == null) {
            outputCtrl.value = "字符串有错误";
            return;
        }
        
        var theResult = StrSubString(theValue, startIndex);

outputCtrl.value = theResult;
    }

</script>

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