How much does gzip save?
Classic script (no import), so the code sits inside an async function. Sizes are the real bytes of the course files.
Later the data will live in cloud storage instead of your project folder. Only one line of config changes, but the browser then enforces CORS, caching and size rules you must understand. Keys and secrets never go in frontend code.
Change the code and press Run (Ctrl+Enter). Predict what will happen first, then break it on purpose and read what changes. Your edits are saved and match the lesson page.
Ready for more? This phase has 5 hands-on exercises with automatic checks.
Practice questions
Write the code in the editor, run it, then open the model answer to compare.
Write dataUrl(base, file) so that dataUrl("/data/lumen", "/daily.csv") and dataUrl("/data/lumen/", "daily.csv") both give /data/lumen/daily.csv.
A teammate sees Failed to fetch for the bucket URL but the file opens in a new tab. Name the likely cause and the first place to look.
Explain it without notes
Why does moving the data to a bucket change only one line of code?
What does the browser do when a response has no Access-Control-Allow-Origin header, and what does your code see?
Why must a secret key never appear in frontend code, and what do you use instead?
Preview
Console
Nothing logged yet.Expected console output
stations.csv 1414 bytes 555 gzipped 39%
daily.csv 13406 bytes 4587 gzipped 34%
hourly-june.csv 19334 bytes 3444 gzipped 18%
trips-10k.csv 487313 bytes 146324 gzipped 30%
bikes.json 24053 bytes 2790 gzipped 12%
routes.json 3932 bytes 661 gzipped 17%
ardenvale.topojson 2684 bytes 1089 gzipped 41%
world-110m.json 107761 bytes 38423 gzipped 36%