minify AT.js execute error: Cannot read property 'substr' of undefined

when I use Esprima(offline) to minify the code, It's not okay when use AT.js. But If I don't use Esprima, all goes well.

Uncaught Error: Cannot read property 'substr' of undefined
at line 1 col 222
...;if(e)for(var c in e)for(;b.substr(0,c.length)==c;)if(a=b,b=...

I think the position of the error right here:

if (line[0]=="\n") {line=line.substr(1);}
    if (handlers) {
      for (var h in handlers) {
        while (line.substr(0,h.length)==h) {
          // console.log("execute handler", h)
          var pre = line;
          line = handlers[h](line);
          if (pre==line) {return;} // handler needs more data
          //if (dbg) console.log("HANDLER] "+JSON.stringify(pre)+"=>"+JSON.stringify(line)+" ("+h+")");
        }
      }
    }

How can I avoid this error?

Otherwise, when I tried to uncheck the Esprima: Mangle(Shorten variable name), the result of this error still use the short variable name, I wonder if WEB IDE didn't work?

=======================================
I tried to write a simple code in WEB-IDE,

Serial2.setup(19200, {rx: A3, tx: A2});
let at = require('AT').connect(Serial2);
//console.log
at.cmd("AT+CIPOPEN?\r\n",1000,function(r){console.log(r)});

and use Esprima to minify the code, like these. It's the same with the original AT.js.

Serial2.on("data", function (d) {if(console.log('res',JSON.stringify(d)),d[0]==='extends typeof'&&(d=d.replace('extends typeof','')),dataCount){if(line&&(d=line+d,line=''),d.length<=dataCount){dataCount-=d.length,dataCallback(d),dataCount==0&&(dataCallback=undefined);return;}dataCallback(d.substr(0,dataCount)),d=d.substr(dataCount),dataCount=0,dataCallback=undefined;}if(line+=d,line[0]=='\n'&&(line=line.substr(1)),handlers)for(var h in handlers)while(line.substr(0,h.length)==h){var pre=line;if(line=handlersh,pre==line)return;}var i=line.indexOf('\r');while(i>=0){var l=line.substr(0,i);var handled=!1;if(l.length>0)for(var h in lineHandlers){let namee='ddddd';l.substr(0,h.length)==h&&(lineHandlersh,handled=!0),handled||lineCallback&&l&&lineCallback(l);}if(line=line.substr(i+1),handled&&dataCount)return cb('');if(line[0]=='\n'&&(line=line.substr(1)),line.length&&handlers)for(var h in handlers)line.substr(0,h.length)==h&&(line=handlersh);line||(line=''),i=line.indexOf('\r');}});

However, when I pick up the same position code from my project by dump(), the AT.js part is different with the previous one.

function Cnet(ua) {
  iam = this;
  uart = ua;
  at = require("AT").connect(ua);
  setTimeout(function () {
    init1();
  }, 3000);
}

Serial2.on("data", function (a) {
if(d){b&&(a=b+a,b="");if(a.length<=d){d-=a.length;l(a);0==d&&(l=void 0);return}l(a.substr(0,d));a=a.substr(d);d=0;l=void 0}b+=a;m&&console.log("] "+JSON.stringify(a));"\n"==b[0]&&(b=b.substr(1));if(e)for(var c in e)for(;b.substr(0,c.length)==c;)if(a=b,b=ec,a==b)return;for(a=b.indexOf("\r");0<=a;){var f=b.substr(0,a),p=!1;if(0<f.length){for(c in h)f.substr(0,c.length)==c&&(hc,p=!0);p||g&&
g(f)}b=b.substr(a+1);if(p&&d)return q("");"\n"==b[0]&&(b=b.substr(1));if(b.length&&e)for(c in e)b.substr(0,c.length)==c&&(b=ec);a=b.indexOf("\r")}
});