dist/event-target-shim.js
function setCancelFlag(data) {
    if (data.passiveListener != null) {
        if (
            typeof console !== "undefined" &&
            typeof console.error === "function"
        ) {
            console.error(
                "Unable to preventDefault inside passive event listener invocation.",
                data.passiveListener
            );
        }
        return
    }
    if (!data.event.cancelable) {
        return
    }

    data.canceled = true;
    if (typeof data.event.preventDefault === "function") {
        data.event.preventDefault();
    }
}
function setCancelFlag(data) {
    if (data.passiveListener != null) {
        if (
            typeof console !== "undefined" &&
            typeof console.error === "function"
        ) {
            console.error(
                "Unable to preventDefault inside passive event listener invocation.",
                data.passiveListener
            );
        }
        return
    }
    if (!data.event.cancelable) {
        return
    }

    data.canceled = true;
    if (typeof data.event.preventDefault === "function") {
        data.event.preventDefault();
    }
}
https://dom.spec.whatwg.org/#set-the-canceled-flag
@param data {PrivateData} private data.