use opencv in node.js with typescript

readme.md

1. download precompile's opencv.js to src/opencv.js
2. download Lenna png to Lenna.png
3. save index.ts and global.d.ts in src/ directory
4. npm run build && npm run cp
5. npm run run

full directory tree:

.
├── Lenna.png
├── README.md
├── output.png
├── package.json
├── src
│   ├── global.d.ts
│   ├── index.ts
│   └── opencv.js
└── tsconfig.json

global.d.ts

declare global {
    /** opencv's export variable */
    var Module: Object
}

export {}

index.ts

import Jimp from 'jimp'

async function onRuntimeInitialized() {
    // load local image file with jimp. It supports jpg, png, bmp, tiff and gif:
    var jimpSrc = await Jimp.read('./Lenna.png')
    // `jimpImage.bitmap` property has the decoded ImageData that we can use to create a cv:Mat
    var src = cv.matFromImageData(jimpSrc.bitmap)
    // following lines is copy&paste of opencv.js dilate tutorial:
    let dst = new cv.Mat()
    let M = cv.Mat.ones(50, 50, cv.CV_8U)
    let anchor = new cv.Point(-1, -1)
    cv.dilate(src, dst, M, anchor, 1, cv.BORDER_CONSTANT, cv.morphologyDefaultBorderValue())
    // Now that we are finish, we want to write `dst` to file `output.png`. For this we create a `Jimp`
    // image which accepts the image data as a [`Buffer`](https://nodejs.org/docs/latest-v10.x/api/buffer.html).
    // `write('output.png')` will write it to disk and Jimp infers the output format from given file name:
    new Jimp({
        width: dst.cols,
        height: dst.rows,
        data: Buffer.from(dst.data),
    }).write('output.png')
    src.delete()
    dst.delete()
}
// Finally, load the open.js as before. The function `onRuntimeInitialized` contains our program.
globalThis.Module = {
    onRuntimeInitialized,
}
const cv: typeof import('mirada') = require('./opencv')

package.json

{
  "name": "cv-hello",
  "module": "index.ts",
  "scripts": {
    "build": "esbuild src/index.ts --outdir=dist --minify --platform=node --format=cjs",
    "cp": "cp src/opencv.js ./dist",
    "run": "node dist/index.js"
  },
  "devDependencies": {
    "esbuild": "^0.19.2",
    "mirada": "^0.0.15"
  },
  "dependencies": {
    "jimp": "^0.22.10"
  }
}

tsconfig.json

{
  "compilerOptions": {
    "lib": ["ESNext"],
    "module": "esnext",
    "target": "esnext",
    "strict": true,
    "allowJs": true,
    "noEmit": true,
    "noImplicitAny": false,
  },
  "include": [
    "src/**/*.ts"
  ]
}