how to do http request in flutter_qjs

[Jackiu1997]

I use XMLHttpRequest and fetch, they all response not defined error.

[mabDc]

I use XMLHttpRequest and fetch, they all response not defined error.

bind function in dart code but not js code.
see following

flutter_qjs/README.md

Lines 140 to 160 in 32aac42

	Since v0.3.0, you can pass a function to `JSInvokable` arguments, and `channel` function is no longer included by default. You can use js function to set dart object globally.
	For example, use `Dio` to implement http in qjs:
	```dart
	final setToGlobalObject = await engine.evaluate("(key, val) => { this[key] = val; }");
	await setToGlobalObject.invoke(["http", (String url) {
	return Dio().get(url).then((response) => response.data);
	}]);
	setToGlobalObject.free();
	```
	In isolate, top level function passed in `JSInvokable` will be invoked in isolate thread. Use `IsolateFunction` to pass a instant function:
	```dart
	await setToGlobalObject.invoke([
	"http",
	IsolateFunction((String url) {
	return Dio().get(url).then((response) => response.data);
	}),
	]);
	```