Tips for soothing the TypeScript compiler

Question

Tips for soothing the TypeScript compiler

It seems like TypeScript is heavily influenced by Microsoft's interpretation of the DOM and JavaScript. But what if I'm not concerned with Internet Explorer and Edge? Unfortunately, I'm encountering issues with TypeScript...

For instance, when using Element.getBoundingClientRect(), it returns an object with x and y properties in most browsers, except for IE and Edge (refer to notes here).

When attempting to compile code where I use this method, such as I encounter a compilation error stating

TS2339: Property 'x' does not exist on type 'ClientRect | DOMRect'.

Is there a way to convince the compiler to overlook these issues?

typescript

Answer 1

Answer №1

When TypeScript infers the type of a variable as A | B, it indicates that the variable is either of type A or B (or something that can be assigned to at least one of those types). This means when you access a variable with this type, only properties present in both types are accessible, as they exist regardless of which type the variable actually is.

In contrast, a variable of type A & B is guaranteed to be both type A and type B. Therefore, all properties from both A and B are available for use.

In certain situations, TypeScript explicitly shows that variables like x and y may not always be available. However, if you are confident that they are, such as knowing your rectangle is a proper DOMRect (or DOMRectReadOnly), you can safely cast the variable to that type:

const rect = elem.getBoundingClientRect() as DOMRect;

If you are uncertain, utilizing type guards can help prevent unchecked casts by implementing code that performs runtime checks to support TypeScript's type inference:

if ('x' in rect) {
    // The property x belongs uniquely to DOMRect and not ClientRect
    // TypeScript now recognizes rect as type DOMRect.
    ...
}

For detailed information, you can explore the complete DOM API types on Microsoft's TypeScript project repository on Github.

Answer 2

When TypeScript infers the type of a variable as A | B, it indicates that the variable is either of type A or B (or something that can be assigned to at least one of those types). This means when you access a variable with this type, only properties present in both types are accessible, as they exist regardless of which type the variable actually is.

In contrast, a variable of type A & B is guaranteed to be both type A and type B. Therefore, all properties from both A and B are available for use.

In certain situations, TypeScript explicitly shows that variables like x and y may not always be available. However, if you are confident that they are, such as knowing your rectangle is a proper DOMRect (or DOMRectReadOnly), you can safely cast the variable to that type:

const rect = elem.getBoundingClientRect() as DOMRect;

If you are uncertain, utilizing type guards can help prevent unchecked casts by implementing code that performs runtime checks to support TypeScript's type inference:

if ('x' in rect) {
    // The property x belongs uniquely to DOMRect and not ClientRect
    // TypeScript now recognizes rect as type DOMRect.
    ...
}

For detailed information, you can explore the complete DOM API types on Microsoft's TypeScript project repository on Github.

Answer 3

Answer №2

To overcome this issue, one solution could be to utilize the concept of interface combination.

interface ClientRect {
    x: number;
}

let button = document.createElement('button');
button.textContent = "Click Here";
document.body.appendChild(button);
let rect = button.getBoundingClientRect();
let xPosition = rect.x; // no problem!
console.log(xPosition);

In TypeScript, when two interfaces share the same name, they will merge together and create a single interface with combined properties such as the x property in ClientRect.

Answer 4

To overcome this issue, one solution could be to utilize the concept of interface combination.

interface ClientRect {
    x: number;
}

let button = document.createElement('button');
button.textContent = "Click Here";
document.body.appendChild(button);
let rect = button.getBoundingClientRect();
let xPosition = rect.x; // no problem!
console.log(xPosition);

In TypeScript, when two interfaces share the same name, they will merge together and create a single interface with combined properties such as the x property in ClientRect.

Tips for soothing the TypeScript compiler

Answer №1

Answer №2

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