Download Progress: Fetch Work

async function downloadWithProgress(url) { const response = await fetch(url); const reader = response.body.getReader(); const contentLength = +response.headers.get('Content-Length'); let receivedLength = 0; let chunks = []; while(true) { const {done, value} = await reader.read(); if (done) break; chunks.push(value); receivedLength += value.length; let progress = (receivedLength / contentLength) * 100; console.log(`Download Progress: ${progress.toFixed(2)}%`); } let chunksAll = new Uint8Array(receivedLength); let position = 0; for(let chunk of chunks) { chunksAll.set(chunk, position); position += chunk.length; } return new Blob([chunksAll]); } Use code with caution. Important Considerations CORS and Headers

Combine the chunks back into a single blob or array for use. Implementation Example javascript download progress fetch

If the server sends compressed data (like Gzip), Content-Length often refers to the compressed size, while the chunks you read in JavaScript are the uncompressed bytes. This can cause the progress to exceed 100%. To fix this, ensure the server sends the uncompressed size or disable compression for those specific assets. Service Workers This can cause the progress to exceed 100%

To implement "download progress fetch" functionality, follow these logic steps: Initiate the fetch request to your URL. Check for a successful response (status 200). Check for a successful response (status 200)

For the Content-Length header to be accessible via JavaScript, the server must be configured with Cross-Origin Resource Sharing (CORS). Specifically, it needs to include Access-Control-Expose-Headers: Content-Length in its response. Without this, the length will return null, making percentage calculations impossible. Gzip and Compression