HTML5ページの長押しで画像を保存する機能を解決するための記事

npm i html2canvas --save
import html2canvas from 'html2canvas';
// The image node you want to save
const dom = document.querySelector('img');
// Create a new canvas
const Canvas = document.createElement('canvas');
const width = document.body.offsetWidth; // the width of the visible screen
const height = document.body.offsetHeight; // the height of the visible screen
const scale = window.devicePixelRadio; // device's devicePixelRadio
// Scale the Canvas canvas and put it in a smaller screen to solve the blur problem
Canvas.width = width * scale;
Canvas.height = height * scale;
Canvas.getContext('2d').scale(scale, scale);
html2canvas(dom, {
  canvas: Canvas,
  scale,
  useCORS: true,
  logging: true,
  width: width + 'px',
  hegiht: height + 'px',
}).then((canvas) => {
  const context = canvas.getContext('2d');
  // turn off anti-aliasing
  context.mozImageSmoothingEnabled = false;
  context.webkitImageSmoothingEnabled = false;
  context.msImageSmoothingEnabled = false;
  context.imageSmoothingEnabled = false;
  // Convert canvas to image
  canvas2Image(canvas, canvas.width, canvas.height);
});

canvas2Image(canvas, canvas.width, canvas.height) {
  const retCanvas = document.createElement('canvas');
  const retCtx = retCanvas.getContext('2d');
  retCanvas.width = width;
  retCanvas.height = height;
  retCtx.drawImage(canvas, 0, 0, width, height, 0, 0, width, height);
  const img = document.createElement('img');
  img.src = retCanvas.toDataURL('image/jpeg'); // you can change the format as needed
  return img;
}

// Wrap a long press method
longPress(fn) {
  let timeout = 0;
  const $this = this;
  for (let i = 0; i < $this.length; i++) {
    $this[i].addEventListener('touchstart', () => {
      timeout = setTimeout(fn, 800); // if the long press time exceeds 800ms, then execute the method passed in 
    }, false);
    $this[i].addEventListener('touchend', () => {
      clearTimeout(timeout); // long press time less than 800ms, will not execute the incoming method
    }, false);
  }
}
// Add the generated image to the body
const img = canvas2Image(canvas, canvas.width, canvas.height);
document.body.appendChild(img);
img.style.cssText = "width:100%;height:100%;position:absolute;top:0;left:0;right:0;bottom:0;openness:0;";

$.fn.longPress = function(fn) {
  let timeout = 0;
  const $this = this;
  for (let i = 0; i < $this.length; i++) {
    $this[i].addEventListener('touchstart', () => {
      timeout = setTimeout(fn, 800); // if the long press time exceeds 800ms, then execute the method passed in 
    }, false);
    $this[i].addEventListener('touchend', () => {
      clearTimeout(timeout); // long press time less than 800ms, will not execute the incoming method
    }, false);
  }
};
$('img').longPress(() => {
  saveImg();
});saveImg() {
  // The image node you want to save
  const dom = document.querySelector('img');
  // Create a new canvas
  const Canvas = document.createElement('canvas');
  const width = document.body.offsetWidth; // the width of the visible screen
  const height = document.body.offsetHeight; // the height of the visible screen
  const scale = window.devicePixelRatio; // device's devicePixelRatio
  // Scale the Canvas canvas and put it in a smaller screen to solve the blur problem
  Canvas.width = width * scale;
  Canvas.height = height * scale;
  Canvas.getContext('2d').scale(scale, scale);
  html2canvas(dom, {
    canvas: Canvas,
    scale,
    useCORS: true,
    logging: true,
    width: width + 'px',
    hegiht: height + 'px',
  }).then((canvas) => {
    const context = canvas.getContext('2d');
    // turn off anti-aliasing
    context.mozImageSmoothingEnabled = false;
    context.webkitImageSmoothingEnabled = false;
    context.msImageSmoothingEnabled = false;
    context.imageSmoothingEnabled = false;
    // canvas to image conversion
    const img = canvas2Image(canvas, canvas.width, canvas.height);
    document.body.appendChild(img);
    img.style.cssText = "width:100%;height:100%;position:absolute;top:0;left:0;right:0;bottom:0;opacity:0;";
  }
}
canvas2Image(canvas, width, height) {
  const retCanvas = document.createElement('canvas');
  const retCtx = retCanvas.getContext('2d');
  retCanvas.width = width;
  retCanvas.height = height;
  retCtx.drawImage(canvas, 0, 0, width, height, 0, 0, width, height);
  const img = document.createElement('img');
  img.src = retCanvas.toDataURL('image/jpeg'); // you can change the format as needed
  return img;
}