How to call a Dart function from Javascript?

Issue

I would like to call a Dart function from Javascript.

I would like to compile a Dart script containing a Dart function using dart2js (version 1.1.3) and then load the generated .js file into a Javascript environment and call that function from Javascript.

Something along the lines of calling myHyperSuperMegaFunction below from Javascript.

import 'dart:js' as js;

int myHyperSuperMegaFunction(int a, int b) {
  return a + b;
}

main() {
  js.context['myHyperSuperMegaFunction'] = new js.JsFunction.withThis(myHyperSuperMegaFunction);
}

I tried compiling the above with dart2js and loading the generated .js file into Chrome. Variable myHyperSuperMegaFunction is registered and defined as

function () {
    return _call(f, captureThis, this, Array.prototype.slice.apply(arguments));
}

However, when I call myHyperSuperMegaFunction(2,3) from Chrome Javascript console I get the following error NoSuchMethodError : method not found: 'Symbol("call")' Receiver: Instance of '(){this.$initialize' Arguments: [Instance of 'Window', 2, 3]

Solution

You don’t need to use new js.JsFunction.withThis. In your case just use :

js.context['myHyperSuperMegaFunction'] = myHyperSuperMegaFunction;

For your information new js.JsFunction.withThis has to be used when you need to use the this Js context. In your error, you can see that the first parameter is Instance of 'Window' which is the global context in Js.

Answered By – Alexandre Ardhuin

Answer Checked By – Jay B. (FlutterFixes Admin)

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