How to use a wildcard when searching a dataset

Here is some code that I'm using:

++++START++++++++++
Search_btn.onPress = function() {
      if (this._parent.ReasonCode_ds.hasSort("Category")) {
      this._parent.ReasonCode_ds.removeSort("Category");
      }
      var SearchID:String = null;
      this._parent.ReasonCode_ds.addSort("Category",["Types"]);
      if (this._parent.ReasonCode_ds.findFirst([this._parent.Search_txt.text])) {
       SearchID = this._parent.ReasonCode_ds.getItemId();
         this._parent.ReasonCode_ds.locateById(SearchID);
      } else {
            this._parent.ReasonCode_ds.removeSort("Category");
      }
      
      
}
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I want to be able to use a wild card when entering text into the --- Search_txt --- component. (i.e. "Lost *")

So, if I have multiple instances in the dataset of the word "Lost" and I want to do a search for all instances normally I would use something like "Lost *", however for some reason if I enter "Lost" or "Lost *" the search fails. I have to put in the exact phrase that is in the dataset before I get a successful search (i.e. "Lost Keys") if "Lost Keys" is one of the items in the data set then the search works.

I sure hope someone out there can help. It doesn't seem logical to have to do a search for an exact phrase when the user may not know what the exact phrase is in the dataset!