How to use the blob function in blob

Object.keys(this.state.files).forEach((key) => {
      const file = this.state.files[key]
      formData.append(key, new Blob([file], { type: file.type }), file.name || 'file')
    })

_downloadTxtFile = () => {
    const { minerPaymentTxSlate } = this.props
    const element = document.createElement('a')
    const file = new Blob([minerPaymentTxSlate], { type: 'text/plain' })
    element.href = URL.createObjectURL(file)
    const date = new Date()
    const timestamp = Math.floor(date.getTime() / 1000)
    element.download = `txSlate-${timestamp}.txt`
    element.click()
  }

onFeed( err, data ) {
		this.setState( {
			disabled: false
		} );

		if ( ! err && ! data.success ) {
			err = new Error( this.translate( 'Error exporting Reader feed' ) );
		}

		if ( err ) {
			this.props.onError( err );
		} else {
			const blob = new Blob( [ data.opml ], { type: 'text/xml;charset=utf-8' } );
			saveAs( blob, this.props.saveAs );
			this.props.onExport( this.props.saveAs );
		}
	},