js关于图片的操作（压缩等）

export default class ImageCompress {
  constructor(file, fileSize, maxWH = 1920) {
    this.file = file
    this.fileSize = fileSize
    this.maxWH = maxWH // 最大长宽
  }

  compress() {
    // 压缩
    const fileType = this.file.type
    const fileSize = this.file.size / 1024
    return new Promise(resolve => {
      const reader = new FileReader()
      reader.readAsDataURL(this.file)
      reader.onload = () => {
        const canvas = document.createElement('canvas')
        const img = document.createElement('img')
        img.src = reader.result
        img.onload = () => {
          const ctx = canvas.getContext('2d')
          const _dWH = this.dWH(