constructor (input, context, globalOptions = {}) {
    this.input = input
    this.fileList = input.files
    this.files = []
    this.options = {
      ...{ mimes: {} },
      ...globalOptions
    }
    this.results = false
    this.context = context
    this.dataTransferCheck()
    if (context && context.uploadUrl) {
      this.options.uploadUrl = context.uploadUrl
    }
    this.uploadPromise = null
    if (Array.isArray(this.fileList)) {
      this.rehydrateFileList(this.fileList)
    } else {
      this.addFileList(this.fileList)
    }
  }
Create a file upload object.
@param {FileList} fileList
@param {object} context