I've been looking into exactly why Webpack is hanging silently. One thing I noticed is that in Webpack 5, since it doesn't include polyfills and globals by default, people have to use the ProvidePlugin for globals like Buffer. However, JSZip uses the existence of Buffer for NodeJS support.

Line 7 in 25d401e

exports.nodebuffer = typeof Buffer !== "undefined";

This was likely already an issue before Webpack 5. The dist build removes Buffer using Browserify which is why it works. But in Webpack 5, it fails to resolve browser in the package.json and falls back to main (which is the fix #742 provides).

There's likely a switch somewhere that switches to a NodeJS stream that never emits events in a browser, causing a silent failure from this hanging promise.

jszip/lib/stream/StreamHelper.js

Lines 77 to 105 in 25d401e

    
           function accumulate(helper, updateCallback) { 
        
               return new external.Promise(function (resolve, reject){ 
        
                   var dataArray = []; 
        
                   var chunkType = helper._internalType, 
        
                       resultType = helper._outputType, 
        
                       mimeType = helper._mimeType; 
        
                   helper 
        
                   .on('data', function (data, meta) { 
        
                       dataArray.push(data); 
        
                       if(updateCallback) { 
        
                           updateCallback(meta); 
        
                       } 
        
                   }) 
        
                   .on('error', function(err) { 
        
                       dataArray = []; 
        
                       reject(err); 
        
                   }) 
        
                   .on('end', function (){ 
        
                       try { 
        
                           var result = transformZipOutput(resultType, concat(chunkType, dataArray), mimeType); 
        
                           resolve(result); 
        
                       } catch (e) { 
        
                           reject(e); 
        
                       } 
        
                       dataArray = []; 
        
                   }) 
        
                   .resume(); 
        
               }); 
        
           }

Anyways, that's why it hangs without an error. Browsers should use the dist build (#742).

	function accumulate(helper, updateCallback) {
	return new external.Promise(function (resolve, reject){
	var dataArray = [];
	var chunkType = helper._internalType,
	resultType = helper._outputType,
	mimeType = helper._mimeType;
	helper
	.on('data', function (data, meta) {
	dataArray.push(data);
	if(updateCallback) {
	updateCallback(meta);
	}
	})
	.on('error', function(err) {
	dataArray = [];
	reject(err);
	})
	.on('end', function (){
	try {
	var result = transformZipOutput(resultType, concat(chunkType, dataArray), mimeType);
	resolve(result);
	} catch (e) {
	reject(e);
	}
	dataArray = [];
	})
	.resume();
	});
	}

Uh oh!

generateAsync doesn't work and there was no error #724

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