[字符串处理]替换字符串中间位置字符为指定字符

示例：

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);
}
},