向字符串对象中追加replaceAll方法

/**
*  向字符串对象中追加replaceAll方法
* @param {} reallyDo
* @param {} replaceWith
* @param {} ignoreCase
* @return {}
*/
String.prototype.replaceAll = function(reallyDo, replaceWith, ignoreCase) {
if (!RegExp.prototype.isPrototypeOf(reallyDo)) {
return this.replace(new RegExp(reallyDo, (ignoreCase ? "gi": "g")), replaceWith);
} else {
return this.replace(reallyDo, replaceWith);
}
}