Question

event: "Deprecated symbol used, consult docs for better alternative"

It's been a while that PyCharm (I suppose it's the same with WebStorm and other JetBrains IDEs) raise a weak warning on the event variables I use in my code.

For instance in the following code

<div id="my-div" onclick="event.preventDefault();">...</div>

PyCharm displays this message "Deprecated symbol used, consult docs for better alternative".

The problem seems to be that the event variable refers to Window.event, and according to MDN Web Docs:

You should avoid using this property in new code, and should instead use the Event passed into the event handler function. This property is not universally supported and even when supported introduces potential fragility to your code.

I know that a correct workaround would be to write in a javascript tag:

document.getElementById("my-div").addEventListener("click", function(event) {
  console.log("And use this " + event + " instead");
});

I am just wondering what would be, if it exists, the correct way to use events in the HTML code (onclick attribute).

46 41716 46

1 Jan 1970

Solution

I do not know if it is still important for someone or not, but tested on WebStorm 2020.3 the following works, and the IDE does not complain about deprecation. Additionally, WebStorm identifies the event as Event.

Code snippet below.

(function() {
    const checkBox = document.querySelector("#id-checkbox");
    checkBox.addEventListener('click', (event) => {
        event.preventDefault();
    }, false);
})();

<head>
    <script src="click.js" defer></script>
</head>
<body>
    <p>Please click on the checkbox control.</p>
    <form>
        <label for="id-checkbox">Checkbox:</label>
        <input type="checkbox" id="id-checkbox"/>
    </form>

    <div id="output-box"></div>
</body>

2021-01-30

Solution

For an on HTML attribute handler, the value of an handler is the body of a function. And if the function is returning false, you will cancel it.

Then, your example should be rewritten

<div id="my-div" onclick="return false;">...</div>

Note that you got the same deprecation notice for the same reason with the definition of a callback in a event listener.

For instance, this code will trigger the same deprecation notice.

element.addEventListener("click", myCallbackFunction(event));

In this case, you should pass an event listener object to remove this deprecation. (ie wrap your callback function in an object and set it into the handleEvent property)

For instance:

let callbackObject = { handleEvent: function(event){...} }
element.addEventListener("click", callBackObject);

2021-10-09