Provide type hints to monaco editor

Question

I am trying to provide intellisense / code completion into a javascript editor using the Monaco editor. The code needs to be valid javascript, not typescript.

Given some

Answer 1

Put this in the editor in the Monaco Playground:

monaco.editor.create(document.getElementById("container"), {
    value: "function hello() {\n\talert('Hello world!');\n}",
    language: "typescript"
});

const fact = `declare function onMyEvent(event: string): void; 
`;
const factFilename = 'myCustomNamespace1';
this.monaco.languages.typescript.typescriptDefaults.addExtraLib(fact, factFilename);

Now when you type onMyEvent in the right-hand pane, you'll get