I have attempted numerous methods, but the TypeScript object remains potentially undefined

Question

I have attempted numerous methods, but the TypeScript object remains potentially undefined

My current code involves using canvas to capture the cropped image. Below is the function that handles this process:

export const getCroppedImg = (
  image: HTMLImageElement,
  crop: Crop,
  fileName: string
): Promise<Blob> => {
  let canvas: HTMLCanvasElement;
  let ctx: CanvasRenderingContext2D;
  // Employing next.js here
  if (typeof window !== "undefined") {
    if (crop) {
      canvas = document.createElement("canvas");
      const scaleX = image.naturalWidth / image.width;
      const scaleY = image.naturalHeight / image.height;
      canvas.width  =crop.width ? crop.width * scaleX : undefined;
      canvas.height =crop.height &&  crop.height * scaleY;
      ctx = canvas.getContext("2d") as CanvasRenderingContext2D;

      ctx.drawImage(
        image,
        crop.x * scaleX,
        crop.y * scaleY,
        crop.width * scaleX,
        crop.height * scaleY,
        0,
        0,
        crop.width * scaleX,
        crop.height * scaleY
      );
    }
  }

The use of

crop.x, crop.y, crop.width crop.height

is triggering a TypeScript error stating "Object is possibly 'undefined'". I attempted two different approaches by wrapping the entire logic with an if(crop).

      canvas.width  =crop.width ? crop.width * scaleX : undefined;
      canvas.height =crop.height &&  crop.height * scaleY;

An issue arises with the warnings for "canvas.width" and "canvas.height":

"Type 'number | undefined' is not assignable to type 'number'.
  Type 'undefined' is not assignable to type 'number'.ts(2322)

Below is the definition for the Crop interface:

import { Crop } from "react-image-crop";

interface Crop {
        aspect?: number;
        x?: number;
        y?: number;
        width?: number;
        height?: number;
        unit?: 'px' | '%';
    }

typescript canvas next.js

Answer 1

Answer №1

Prior to checking, it is recommended to extract the values of crop.width and crop.height into separate variables.

Avoid assigning undefined to canvas.width, instead of using && for conditional assignments, utilize if.

If any of the properties of crop are undefined, like width or height, it is best not to proceed with the logic to prevent errors in canvas drawing or drawImage.

In addition, omit the Promise<Blob> type as a Promise is not being returned in this function.

export const getCroppedImg = (
    image: HTMLImageElement,
    crop: Crop,
) => {
    const { width, height, x, y } = crop;
    if (typeof window === "undefined" || !width || !height || !x || !y) {
        // Proceeding further would make no sense;
        // can't adjust canvas, or draw the image
        // return here, or throw an error or something
        throw new Error('Bad argument');
    }
    const canvas = document.createElement("canvas");
    const scaleX = image.naturalWidth / image.width;
    const scaleY = image.naturalHeight / image.height;

    canvas.width = width * scaleX;
    canvas.height = height * scaleY;
    const ctx = canvas.getContext("2d") as CanvasRenderingContext2D;

    ctx.drawImage(
        image,
        x * scaleX,
        y * scaleY,
        width * scaleX,
        height * scaleY,
        0,
        0,
        width * scaleX,
        height * scaleY
    );
}

Answer 2

Prior to checking, it is recommended to extract the values of crop.width and crop.height into separate variables.

Avoid assigning undefined to canvas.width, instead of using && for conditional assignments, utilize if.

If any of the properties of crop are undefined, like width or height, it is best not to proceed with the logic to prevent errors in canvas drawing or drawImage.

In addition, omit the Promise<Blob> type as a Promise is not being returned in this function.

export const getCroppedImg = (
    image: HTMLImageElement,
    crop: Crop,
) => {
    const { width, height, x, y } = crop;
    if (typeof window === "undefined" || !width || !height || !x || !y) {
        // Proceeding further would make no sense;
        // can't adjust canvas, or draw the image
        // return here, or throw an error or something
        throw new Error('Bad argument');
    }
    const canvas = document.createElement("canvas");
    const scaleX = image.naturalWidth / image.width;
    const scaleY = image.naturalHeight / image.height;

    canvas.width = width * scaleX;
    canvas.height = height * scaleY;
    const ctx = canvas.getContext("2d") as CanvasRenderingContext2D;

    ctx.drawImage(
        image,
        x * scaleX,
        y * scaleY,
        width * scaleX,
        height * scaleY,
        0,
        0,
        width * scaleX,
        height * scaleY
    );
}

Answer 3

Answer №2

It is mentioned in this line that canvas.width may possibly be undefined:

canvas.width = crop.width ? crop.width * scaleX : undefined;

To avoid this scenario, you can refine the logic accordingly. However, there are instances where your knowledge surpasses that of the TypeScript compiler. In such cases, if you are certain that the value will never be undefined when accessed, you can assert the value.

canvas.width as number

Answer 4

It is mentioned in this line that canvas.width may possibly be undefined:

canvas.width = crop.width ? crop.width * scaleX : undefined;

To avoid this scenario, you can refine the logic accordingly. However, there are instances where your knowledge surpasses that of the TypeScript compiler. In such cases, if you are certain that the value will never be undefined when accessed, you can assert the value.

canvas.width as number

Answer 5

Answer №3

What is the reasoning behind including optional fields in the Crop interface?

Have you experimented with implementing this interface in your code?:

interface Crop {
    aspect: number;
    x: number;
    y: number;
    width: number;
    height: number;
    unit: 'px' | '%';
}

Answer 6

What is the reasoning behind including optional fields in the Crop interface?

Have you experimented with implementing this interface in your code?:

interface Crop {
    aspect: number;
    x: number;
    y: number;
    width: number;
    height: number;
    unit: 'px' | '%';
}

I have attempted numerous methods, but the TypeScript object remains potentially undefined

Answer №1

Answer №2

Answer №3

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