Property 'offsetWidth' does not exist on type 'Element' (TS)

Property 'offsetWidth' does not exist on type 'Element' (TS) #

The error "Property 'offsetWidth' does not exist on type 'Element'" occurs when we try to access the offsetWidth property on an element that has a type of Element. To solve the error, use a type assertion to type the element as HTMLElement before accessing the property.

property offsetwidth not exist type element

This is the index.html file for the examples in this article.

index.html

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<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8" />
  </head>
  <body>
    <div id="box">Box 100</div>

    <script src="./src/index.ts"></script>
  </body>
</html>

And here is an example of how the error occurs in the index.ts file.

src/index.ts

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// 👇️ const box: Element | null
const box = document.querySelector('#box');

if (box != null) {
  // ⛔️ Property 'offsetWidth' does not exist on type 'Element'.ts(2339)
  const offsetWidth = box.offsetWidth;
  console.log(offsetWidth);
}

The reason we got the error is because the return type of the document.querySelector method is Element | null and the offsetWidth property doesn't exist on the Element type.

To solve the error, use a type assertion to type the element as an HTMLElement.

src/index.ts

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const box = document.querySelector('#box') as HTMLElement | null;

if (box != null) {
  const offsetWidth = box.offsetWidth;
  console.log(offsetWidth); // 👉️ 1448
}

If you used the document.getElementsByClassName method, type the collection as HTMLCollectionOf<HTMLElement>.

src/index.ts

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// 👇️ with getElementsByClassName
// type as HTMLCollectionOf<HTMLElement>
const boxes = document.getElementsByClassName(
  'box',
) as HTMLCollectionOf<HTMLElement>;

for (let i = 0; i < boxes.length; i++) {
  const offsetWidth = boxes[i].offsetWidth;
  console.log(offsetWidth);
}

We could have also been more specific and typed the element as HTMLDivElement, because we're working with a div in the example.

Type assertions are used when we have information about the type of a value that TypeScript can't know about.

We effectively tell TypeScript that the box variable stores anHTMLElement or a null value and not to worry about it.

We used a union type to specify that the variable could still be null, because if an HTML element with the provided selector does not exist in the DOM, the querySelector() method returns a null value.

We used a simple if statement that serves as a type guard to make sure the box variable doesn't store a null value before accessing its offsetWidth property.

src/index.ts

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const box = document.querySelector('#box') as HTMLElement | null;

// 👉️ box has type of HTMLElement or null here

if (box != null) {
  // 👉️ box has type of HTMLElement here
  const offsetWidth = box.offsetWidth;
  console.log(offsetWidth); // 👉️ 1448
}

TypeScript knows that the box variable has a type of HTMLElement in the if block and allows us to directly access its offsetWidth property.

It's always a best practice to include null in the type assertion, because the querySelector method would return null if no element with the provided selector was found.

You might also use the optional chaining (?.) operator to short-circuit if the reference is equal to null or undefined

src/index.ts

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const box = document.querySelector('#box') as HTMLElement | null;

const offsetWidth = box?.offsetWidth;
console.log(offsetWidth); // 👉️ 1448

The optional chaining operator short-circuits returning undefined if the reference is equal to null or undefined.

In other words, if the box variable stores a null value, we won't attempt to access the offsetWidth property on null and get a runtime error.

Property 'offsetWidth' does not exist on type 'Element' (TS)

Property 'offsetWidth' does not exist on type 'Element' (TS) #

Borislav Hadzhiev