test.js

function foo1() {
	throw new Error();
}

function foo2() {
	try {
		foo1();
	}
	catch (e) {
		throw e;
	}
}

function foo3() {
	try {
		foo2();
	}
	finally {
	}
}
function foo4() {
	try {
		foo3();
	}
	finally {
	}
}

foo4();

backtrace is rebuilt every time it is rethrown:

diff --git a/quickjs.c b/quickjs.c
index 4392020..00b19cb 100644
--- a/quickjs.c
+++ b/quickjs.c
@@ -5923,7 +5923,14 @@ JSValue JS_Throw(JSContext *ctx, JSValue obj)
 {
     JS_FreeValue(ctx, ctx->current_exception);
     ctx->current_exception = obj;
-    ctx->exception_needs_backtrace = JS_IsError(ctx, obj);
+    if (JS_IsError(ctx, obj)) {
+        JSValue stack = JS_GetProperty(ctx, obj, JS_ATOM_stack);
+        ctx->exception_needs_backtrace = JS_IsUndefined(stack);
+        JS_FreeValue(ctx, stack);
+    }
+    else {
+        ctx->exception_needs_backtrace = FALSE;
+    }
     js_debugger_exception(ctx);
     return JS_EXCEPTION;
 }

This is correct.

Mac-3:quickjs-2019-10-27$ ./qjs test.js
Error
    at foo1 (test.js:2)
    at foo2 (test.js:7)
    at foo3 (test.js:15)
    at foo4 (test.js:22)
    at <eval> (test.js:28)

@koush
Thanks man, this fix helps a lot <3