JPEG bytes JavaScript bytes !== ~170KB ~170KB Network Transmission main-javascript-bundle.js photo.jpg 3.4 s 170KB 3.4 s 170KB Resource Processing Flame Chart Bottom-Up Call Tree Event Log Group by URL Filter Main Image Decode (phone.jpg) Ra...t R...t R...t R...F Self Time Total Time Activity 64.90 ms Image Decode (phone.jpg) 1997.0 ms 44.6 % ▼ native V8Runtime 1997.0 ms 44.6 % Compile 608.9 ms 13.6 % 937.6 ms 20.9 % 6.8 % 6.9 % 303.6 ms 310.3 ms Parse ~2s in Parse/Compile 0.064s in Image Decode Rasterize Paint Ra...t Ra...t ~1.5s in Execution 0.028s in Rasterize Paint @addyosmani - 170KB of (compressed) JS vs. JPEG bytes over a slow 3G network on a Moto G4. JS needing parsed is even larger once decompressed.