FileStore.ts

import { Observable } from 'rxjs';

export class BasicFileInformation {
    public fileName: String;
    public fileSize: Number;
    public fileData: String | ArrayBuffer;
    public fileMimeType: String;

    constructor(fileName: String, fileSize: Number, fileData: String | ArrayBuffer, fileMimeType: String) {
        this.fileName = fileName;
        this.fileSize = fileSize;
        this.fileData = fileData;
        this.fileMimeType = fileMimeType;
    }
}

export abstract class FileStore {
    public static sotreFiles(fileArray: Array<File>): Observable<Array<BasicFileInformation>> {
        const files = [...fileArray];

        return new Observable(obs => {
            const dataURLArray: Array<any> = new Array();

            files.forEach((file: File) => {
                const fileReader: FileReader = new FileReader();
                fileReader.onload = () => {
                    const basifFileInformation = new BasicFileInformation(file.name, file.size, fileReader.result, file.type);
                    dataURLArray.push(basifFileInformation);

                    // Once we know that the array's match in length, call obs.complete. 
                    if (files.length === dataURLArray.length) {
                        obs.next(dataURLArray as Array<any>);
                        obs.complete();
                    }
                };

                fileReader.readAsDataURL(file);
            });
        });
    }

    public static loadFiles(fileArray: Array<BasicFileInformation>): Observable<Array<File>> {
        const files = [...fileArray];
        const tempFileArray = [];

        return new Observable(obs => {
            files.forEach((basicFile: BasicFileInformation) => {
                const name: any = basicFile.fileName;
                const mimeType: any = {
                    type: basicFile.fileMimeType
                };
                const url: any = basicFile.fileData;

                fetch(url)
                    .then(r => r.arrayBuffer())
                    .then(buf => new File([buf], name, mimeType))
                    .then(file => tempFileArray.push(file))
                    .then(() => {
                        obs.next(tempFileArray as Array<any>);
                        obs.complete();
                    });
            });
        });
    }
}