What is the proper way to type the SubmitEvent so that the event.target.children property can be accessed

Below is the form I currently have:

<form id="search" method="post">
<input type="text" name="query" id="search-field"/>
</form>

I am looking to add a submit event listener in TypeScript:

document.getElementById("search").addEventListener("submit", (event: SubmitEvent) => {
        event.preventDefault();
        console.log(event.target.children.query.value);
    });

However, TypeScript is throwing an error:

error TS2339: Property 'children' does not exist on type 'EventTarget'.

20    console.log(event.target.children.query.value);

Is there a way to let TypeScript know that the target of the submit event is a form with a valid children.query element?

Answer №1

When dealing with events that can occur on any HTML element, TypeScript may have difficulty determining which element triggered the event. To assist TypeScript in this scenario, a type assertion can be used. While it may not be considered elegant and might feel somewhat forced, it can be effective when you are certain that your event will only be triggered by a specific HTML element.

By employing this approach, your code could resemble something like the following (with some adjustments made after considering types):

document.getElementById("search").addEventListener("submit", (event: SubmitEvent) => {
    const form = event.target as HTMLFormElement;
    event.preventDefault();
    console.log((form.children.namedItem("search-field") as HTMLInputElement).value);
});

It's important to note that the return value of namedItem is of the type Element, which is quite generic. This necessitated casting it to HTMLInputElement, which in this context contains a value.

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