JavaScript

[HttpPost]
        public FileContentResult Post([FromForm] string communityName, [FromForm] string files)
        {
           
            var removedInvalidCharsFromFileName = removeInvalidCharsFromFileName(files);
               
            var tFiles = removedInvalidCharsFromFileName.Split(',');
            string rootPath = Configuration.GetValue<string>("ROOT_PATH");
            string communityPath = rootPath + "\\" + communityName;

            byte[] theZipFile = null;

            using (MemoryStream zipStream = new MemoryStream())
            {
                using (ZipArchive zip = new ZipArchive(zipStream, ZipArchiveMode.Create, true))
                {
                    foreach (string attachment in tFiles)
                    {
                        var zipEntry = zip.CreateEntry(attachment);

                        using (FileStream fileStream = new FileStream(communityPath + "\\" + attachment, FileMode.Open))
                        using (Stream entryStream = zipEntry.Open())
                        {
                            fileStream.CopyTo(entryStream);
                        }
                    }
                }
                theZipFile = zipStream.ToArray();
            }

            return File(theZipFile, "application/zip", communityName + ".zip");
        }

handleDownload = (e) => {
        e.preventDefault();

        var formData = new FormData();
        formData.append('communityname', this.state.selectedCommunity);
        formData.append('files', JSON.stringify(this.state['checkedFiles']));        
     
        let url = clientConfiguration['filesApi.local'];

        axios({
            method: 'post',
            url: url,
            data:  formData
        });

        window.open(url, '_blank');
    }

handleDownload = (e) => {
        e.preventDefault();

        var formData = new FormData();
        formData.append('communityname', this.state.selectedCommunity);
        formData.append('files', this.state['files']);
        
        alert(this.state['files'].join(','));
        let url = clientConfiguration['filesApi.local'];

        axios({
            method: 'post',
            url: url,
            data:  formData
        });
    }

handleDownload(e) {
        e.preventDefault();
        alert('Hi');
        let communityName = this.state['selectedCommunity'];
        let files = this.state[files];

        fetch(clientConfiguration['filesApi.local'], {
            method: 'POST',
            headers: new Headers(),
            body: JSON.stringify({ communityName: communityName, body: files })
        }).then((res) => res.json())
            .then((data) => console.log(data))
            .catch((err) => console.log(err))
    };

I have a button as below:

        renderDownloadButton() {
        if (this.state.files && this.state.files.filter(i => i.checked).length) {
            return (
                <button id="download" styles="display: none;" onClick={this.handleDownload} >
                    Download
        </button>
            );
        }
    };

let communityName = this.state['selectedCommunity'];

Can not read property state undefined

handleDDLCommunityChange = event => {
    this.setState(
        {
            selectedCommunity: event.target.value
        });

    if (event.target.value == "") {
        this.setState(
            {
                files: null
            });
    }
    else {
        fetch(clientConfiguration['filesApi.local'] + '/' + event.target.value)
            .then((response) => { return response.json(); })
            .then(data => {
                this.setState({
                    files: data.map(file => {
                        return {
                            fileName: file,
                            checked: false
                        }
                    })
                })
            })
            .catch(error => {
                console.log(error);
                debugger;
            });
    }

};

After huge research, i am thinking to build with JavaScript - Search engine with Angular/Vue.js/Meteor/React as front-end

Choice of javascript client side storage is below

1) IndexedDB
2) JScene
3) LargeLocalStorage
4) ydn db
5) PouchDB

Couple of Links

https://github.com/tantaman/LargeLocalStorage
https://gist.github.com/inexorabletash/a279f03ab5610817c0540c83857e4295
http://lintool.github.io/JScene/
https://db-engines.com/en/system/LokiJS%3BPouchDB%3BSolr

Please kindly suggest which one would be best suited...

Basically planning to built a cross platform system which accepts huge files from the user and finally does a full text search...

In this way, the user just needs the browser no installation is required......

In this way, the application will be purely portable irrespective of OS....

This would be absolutely cross platform

Featurs trying to build once the files got indexed by the front-end code/logic

1) Search Box with type-ahead search
2) Combo box to choose the language
3) Number of hits should be while typing. Please type some text in and 
   you will understand what is number of hits
4) Search keyword should be highlighted in the left with portion of text.
   On clicking the text, the entire subject with highlighted search
   should shown in the right
nearly 2,000 files are in text format of 600 kB each size.

the files can be anything - log file or any text file....If support other formats also it is well and good

Please kindly advice with suggestions or comments... As this will benefit for many...

I never come across several open source apps which does full text search or have the functionality which does everything in front-end or client-side

Thanks.