[字符串处理]替换字符串中间位置字符为指定字符

  示例：

            $.fl.stringReplace('12345678', {start: 2, end: 2}) # 12****78

            $.fl.stringReplace('12345678', {format: '-'}) # 12----78

    stringReplace: function(str, opt) {
        var endStr, middleStr, middleStrReplace, options, startStr;
        options = {
            format: (opt != null ? opt.format : void 0) || "*",
            start: (opt != null ? opt.start : void 0) || 1,
            end: (opt != null ? opt.end : void 0) * -1 || 1 * -1
        };
        startStr = str.slice(0, options.start);
        middleStr = str.slice(options.start, options.end);
        endStr = str.slice(options.end);
        middleStrReplace = new Array(middleStr.length + 1).join(options.format);
        if (str.length > 2) {
            return startStr + middleStrReplace + endStr;
        } else {
            return new Array(str.length + 1).join(options.format);
        }
    },