1.直接调用

///js func
function invoke(index, success, fail){
		if(index > 1) {
			success('succes');
		} else {
			fail('fail');
		}
}

/// dart
@JS('invoke')
external static invoke(int index, void Function(String res) success, void Function(String err) fail);

///调用
invoke(2, allowInterop((res){
	print(res);
}), allowInterop((err){
	print(err);
}));

2.转为Promise

///js func
function invoke(index, success, fail){
		if(index > 1) {
			success('succes');
		} else {
			fail('fail');
		}
}
function invokePromise(){
	return new Promise((resolve, reject)=>{
			if(index > 1) {
				resolve('succes');
			} else {
				reject('fail');
			}
   });
}

/// dart
@JS()
abstract class Promise<T> {}

@JS('invoke')
external static invoke(int index, void Function(String res) success, void Function(String err) fail);

external static Promise invokePromise(int index);

static Future invokeJsPromise() {
    final jsPromise = invokePromise();
    return promiseToFuture(jsPromise);
  }

///调用
try {
	final res = await invokeJsPromise(2);
	print(res);
} catch(e, stack){
	print(e);
	print(stack);
}

3.转为Future(推荐)

///js func
function invoke(index, success, fail){
		if(index > 1) {
			success('succes');
		} else {
			fail('fail');
		}
}

///dart
@JS('invoke')
external static invoke(int index, void Function(String res) success, void Function(String err) fail);

static Future invokeFuture(int index) {
    Completer completer = Completer();
    invoke(index, allowInterop((res) {
      completer.complete(res);
    }), allowInterop((err) {
      completer.completeError(err);
    }));
    return completer.future;
  }
///调用
try {
	final res = await invokeFuture(2);
	print(res);
} catch(e, stack){
	print(e);
	print(stack);
}