Problem with arrow function with Bangle.js

Good morning,

Look at this code, it draws 2 horizontal lines on the Bangle screen

function Test(){
  this.p1 = {x:0, y:80};
  this.p2 = {x:240, y:80};
}

Test.prototype.draw = _=> {
  g.clear();
  g.drawLine(0,80,240,80);
};

var t= new Test();
t.draw();
g.drawLine(0,160,240,160);

When it is sent to the emulator, it works well.
When it is sent to the Bangle, it does not work properly, only the second line is drawn.
A dump to the console shows that the function draw() is not properly loaded

dump()
function Test() {this.p1={x:0,y:80},this.p2={x:240,y:80};}
Test.prototype.draw = function (undefined) {return g.clear()};
var t = Object.create(Test["prototype"]);
t.p1 = { "x": 0, "y": 80 };
t.p2 = { "x": 240, "y": 80 };
E.setFlags({ "deepSleep": 0, "pretokenise": 1, "unsafeFlash": 0, "unsyncFiles": 0 });

If I type this code in REPL mode with Bangle connected, it works well.

Where's the error ?