Helper to iterate over file in browser using for-await-of loop

IterableFile.ts

interface IConfig{
    chunkSize:number
}
class IterableFile implements AsyncIterable<string>{
    private reader : FileReader;
    private file:File
    private config : IConfig = {chunkSize : 64 * 1024}

    constructor( file:File,config :Partial<IConfig> = {}){
        this.file = file 
        this.reader = new FileReader(); 
        Object.assign(this.config, config)
    }

    [Symbol.asyncIterator]() {
        return this.readFile();
    }

    get chunkSize(){
        return this.config.chunkSize;
    }

    get fileSize(){
        return this.file.size;
    }

    readBlobAsText(blob) : Promise<string>{
        return new Promise((resolve,reject)=>{
            this.reader.onload = (e:any)=>{
                e.target.result && resolve(e.target.result);
                e.target.error && reject(e.target.error);
            };
            this.reader.readAsText(blob);
        })
    }

    async* readFile() {
        let offset = 0;  
        let blob;
        let result;  
        while(offset < this.fileSize){
            blob = this.file.slice(offset, this.chunkSize + offset);
            result = await this.readBlobAsText(blob);
            offset += result.length;
            yield result;
        }
    }
}
                                      
//  ***Usage***                                       
//  let it = new IterableFile(file)
//  for await (const chunk of it) {
//      console.log(chunk)
//  }