How chrome pages communicate with extensions

as shown in the figure, the web page has btn, and clicking btn will open the corresponding extension a. How to implement

Web page:

a

Thank you!

/ / Please paste the code text below (do not replace the code with pictures)

Mar.29,2021

chrome-extension://

it would be nice for your extension to provide a global variable in the page.

window.__myExtension  = {
    openView() {
        // do something
    }
}

when you click btn, you only need to call _ _ myExtension.openView ()

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