URL Encoding Javascript

Hello,

I am trying to Encode a Text Field within a javascript function. 
The way I have it, it breaks the URL after any special character so its messing up my query.
If anyone has any experience with this please feel free to comment and assist. 


Thank You. 

var span_val = $("span#FIELD_TO_ENCODE").html();
var url = "";         
       url += "https://rxnb.quickbase.com/db/bqk9ep9fj";             
       url += "?act=API_AddRecord";             
       url += "&apptoken="+qbAppToken;             
       url += "&_fid_7=URLEncode("+span_val;                       
       url += "&_fid_6="+ order_ID;