一文彻底解决HTML5页面中长按保存图片功能

npm i html2canvas --save
import html2canvas from 'html2canvas';
// 想要保存的图片节点
const dom = document.querySelector('img');
// 创建一个新的canvas
const Canvas = document.createElement('canvas');
const width = document.body.offsetWidth;  // 可见屏幕的宽
const height = document.body.offsetHeight;  // 可见屏幕的高
const scale = window.devicePixelRadio;  // 设备的devicePixelRadio
// 将Canvas画布放大scale倍，然后放在小的屏幕里，解决模糊问题
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');
  // 关闭抗锯齿形
  context.mozImageSmoothingEnabled = false;
  context.webkitImageSmoothingEnabled = false;
  context.msImageSmoothingEnabled = false;
  context.imageSmoothingEnabled = false;
  // canvas转化为图片
  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');  // 可以根据需要更改格式
  return img;
}

// 封装一个长按方法
longPress(fn) {
  let timeout = 0;
  const $this = this;
  for (let i = 0; i < $this.length; i++) {
    $this[i].addEventListener('touchstart', () => {
      timeout = setTimeout(fn, 800); // 长按时间超过800ms，则执行传入的方法 
    }, false);
    $this[i].addEventListener('touchend', () => {
      clearTimeout(timeout); // 长按时间少于800ms，不会执行传入的方法
    }, false);
  }
}
// 添加生成的图片到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;opacity: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); // 长按时间超过800ms，则执行传入的方法 
    }, false);
    $this[i].addEventListener('touchend', () => {
      clearTimeout(timeout); // 长按时间少于800ms，不会执行传入的方法
    }, false);
  }
};
$('img').longPress(() => {
  saveImg();
});saveImg() {
  // 想要保存的图片节点
  const dom = document.querySelector('img');
  // 创建一个新的canvas
  const Canvas = document.createElement('canvas');
  const width = document.body.offsetWidth;  // 可见屏幕的宽
  const height = document.body.offsetHeight;  // 可见屏幕的高
  const scale = window.devicePixelRatio;  // 设备的devicePixelRatio
  // 将Canvas画布放大scale倍，然后放在小的屏幕里，解决模糊问题
  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');
    // 关闭抗锯齿形
    context.mozImageSmoothingEnabled = false;
    context.webkitImageSmoothingEnabled = false;
    context.msImageSmoothingEnabled = false;
    context.imageSmoothingEnabled = false;
    // canvas转化为图片
    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');  // 可以根据需要更改格式
  return img;
}