前端实现图片压缩（两种方法）

样例3：
// img.onload = () => {
    //   const originWidth = img.width;
    //   const originHeight = img.height;
    //   const maxWidth = 1600;
    //   const maxHeight = 1200;
    //   let targetWidth = originWidth;
    //   let targetHeight = originHeight;
    //   if (originWidth > maxWidth || originHeight > maxHeight) {
    //     if (originWidth / originHeight > maxWidth / maxHeight) {
    //       // 更宽，按照宽度限定尺寸
    //       targetWidth = maxWidth;
    //       targetHeight = Math.round(maxWidth * (originHeight / originWidth));
    //     } else {
    //       targetHeight = maxHeight;
    //       targetWidth = Math.round(maxHeight * (originWidth / originHeight));
    //     }
    //   };
    //   // canvas对图片进行缩放
    //   canvas.width = targetWidth;
    //   canvas.height = targetHeight;
    //
    //   // 清除画布
    //   context.clearRect(0, 0, targetWidth, targetHeight);
    //   // 图片压缩
    //   context.drawImage(img, 0, 0, targetWidth, targetHeight);
    //   canvas.toBlob(
    //     blob => {
    //       console.log('beibeippppp', blob);// blob {size:31784, type: "image/jpeg"}
    //       setCanvasToBlob(blob);
    //     },
    //     'image/jpeg',
    //     0.7,
    //   );
    //   // const imageData = context.getImageData(0, 0, canvas.width, canvas.height);
    //   // const code = jsQR(imageData.data, imageData.width, imageData.height);
    // };
    // img.onerror = () => console.error('Upload file of image format please.');

样例1：
import React from 'react';
import {ImagePicker, Toast} from 'antd-mobile';
import './style.less';


const BznImagesPicker = (props) => {

  const maxSize = 3027;

  const handleChange = (files, operationType, index) => {
    if (operationType === 'add') {
      const file = [...files].pop().file;
      if (file.size > 3 * 1024 * 1024) {
        let rate = 0.6;
        let reader = new FileReader();
        reader.readAsDataURL(file);
        let img = new Image();
        reader.onload = function (e) {
          img.src = e.target.result;
        };
        img.onload = function () {
          let canvas = document.createElement('canvas');
          let context = canvas.getContext('2d');
          // 文件大小KB
          const fileSizeKB = Math.floor(file.size / 1024);
          // console.log('file size：', fileSizeKB, 'kb');
          // 配置rate和maxSize的关系
          if (fileSizeKB * rate > maxSize) {
            rate = Math.floor(maxSize / fileSizeKB * 10) / 10;
            // console.log('file rate：', rate);
            // console.log('file size*rate：', fileSizeKB * rate, 'kb');
          }
          // 缩放比例，默认0.5
          let targetW = canvas.width = this.width * rate;
          let targetH = canvas.height = this.height * rate;
          context.clearRect(0, 0, targetW, targetH);
          context.drawImage(img, 0, 0, targetW, targetH);
          canvas.toBlob(function (blob) {
            const newImage = new File([blob], file.name, {type: file.type});
            // console.log(newImage.size / 1024, 'kb');
            props.onChange && props.onChange([{file: newImage}], operationType, index);
          });
        };
      } else {
        props.onChange && props.onChange(files, operationType, index);
      }
    } else {
      props.onChange && props.onChange(files, operationType, index);
    }
  };

  const handleImageClick = (index, files) => {
    props.onImageClick && props.onImageClick(index, files);
  };

  return (
    !props.hidden
      ? <div className='imagePickerItem'>
        {
          props.label ? <div className='imagePickerLabel'>{props.label}</div> : ''
        }
        <ImagePicker
          files={props.files}
          onChange={handleChange}
          onImageClick={handleImageClick}
          selectable={props.files.length < props.filesLength}
          multiple={props.multiple}
        />
      </div> : ''
  );
};

export default BznImagesPicker;



样例二：
img.onload = () => {
        const originWidth = img.width;
        const originHeight = img.height;
        const maxWidth = 1600;
        const maxHeight = 1200;
        let targetWidth = originWidth;
        let targetHeight = originHeight;
        if (originWidth > maxWidth || originHeight > maxHeight) {
          if (originWidth / originHeight > maxWidth / maxHeight) {
            // 更宽，按照宽度限定尺寸
            targetWidth = maxWidth;
            targetHeight = Math.round(maxWidth * (originHeight / originWidth));
          } else {
            targetHeight = maxHeight;
            targetWidth = Math.round(maxHeight * (originWidth / originHeight));
          }
        }
        // canvas对图片进行缩放
        canvas.width = targetWidth;
        canvas.height = targetHeight;

        // 清除画布
        context.clearRect(0, 0, targetWidth, targetHeight);
        // 图片压缩
        context.drawImage(img, 0, 0, targetWidth, targetHeight);
        canvas.toBlob(
          blob => {
            const newImage = new File([blob as any], (imageFile as any).name, { type: (imageFile as any).type });
            console.log('beibeicai2222blob', blob, newImage); // blob {size:31784, type: "image/jpeg"}
            // setCanvasToBlob(blob);
          },
          (imageFile as any).type,
          0.7,
        );
      };
      img.onerror = () => console.error('Upload file of image format please.');