CODEWITHSUNDEEP
javascripttypescript
FelHa
FelHa

Reputation: 1103

Typechecking throws error in VSCode in regular JS-File

Let's say i have a HTML element as following:

<progress value="1" max="10" id="site_progress"></progress>

VSCode shows a problem ('Property "max" does not exist on type "Element"'), if i select this element like this:

const progress = document.querySelector('#site_progress');
progress.max = 9;

There will be no problems, if i select via element selector:

const progress = document.querySelector('progress');
progress.max = 9;

Can i do something like type assertion to avoid this kind of behavior or what are good practises to handle this problem in regular javascript?

Upvotes: 2

Views: 83

Answers (1)

Keith
Keith

Reputation: 24191

Personally I would just move to TS, but even then you would still need to cast. To cast the type in JS you can do ->

/** @type HTMLProgressElement */
const progress = document.querySelector('#id');
progress.max = 9;

In Typescript it would have been like ->

const progress = document.querySelector('#id') as HTMLProgressElement;
progress.max = 9;

Another nice feature, you can create type guards, and this also helps the compiler.

eg, this below will work in both TS & JS.

const progress = document.querySelector('#id');
if (progress instanceof HTMLProgressElement)
    progress.max = 9;

One slight issue with the above, is if #id is not a Progress it will silently continue. So another option is to throw an exception, this also acts as a type guard, but allows you to throw logical error messages when things are not right.

eg..

const progress = document.querySelector('#id');
if (!(progress instanceof HTMLProgressElement))
  throw new Error('#id not a progress');
progress.max = 9;

Upvotes: 4

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