Typescript
async resizeImg(file: Blob): Promise<Blob> {
let img = document.createElement("img");
img.src = await new Promise<any>(resolve => {
let reader = new FileReader();
reader.onload = (e: any) => resolve(e.target.result);
reader.readAsDataURL(file);
});
await new Promise(resolve => img.onload = resolve)
let canvas = document.createElement("canvas");
let ctx = canvas.getContext("2d");
ctx.drawImage(img, 0, 0);
let MAX_WIDTH = 1000;
let MAX_HEIGHT = 1000;
let width = img.naturalWidth;
let height = img.naturalHeight;
if (width > height) {
if (width > MAX_WIDTH) {
height *= MAX_WIDTH / width;
width = MAX_WIDTH;
}
} else {
if (height > MAX_HEIGHT) {
width *= MAX_HEIGHT / height;
height = MAX_HEIGHT;
}
}
canvas.width = width;
canvas.height = height;
ctx = canvas.getContext("2d");
ctx.drawImage(img, 0, 0, width, height);
let result = await new Promise<Blob>(resolve => { canvas.toBlob(resolve, 'image/jpeg', 0.95); });
return result;
}