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2. Start the Emulator

The SWA Emulator is run by using the swa start command.

  • It runs on http://localhost:4280 by default.
  • Read the swa start documentation for more command details.

2.1 Serve from the current folder

By default, the CLI starts and serves any the static content from the current working directory:

swa start

2.2 Serve from a specified folder

You can override the behavior to start the emulator with a different static assets folder. For instance, if your application artifacts are in ./my-dist then use:

swa start ./my-dist

2.3 Serve from dev server

When developing your SWA front-end, you may want to use the front-end framework's default dev server (started using its CLI) to get benefits like live reload and hot module replacement (HMR).
For Example: Angular devs may use ng serve or npm start to run that dev server.

SWA CLI can reverse proxy requests to that dev server, allowing you to retain the above benefits during the local development of your SWA. You can achieve this in two steps:

  1. Start the local dev server as usual. Note the URL (localhost:port) the dev server runs on.
  2. Start the SWA CLI in a new terminal with the dev server URL specified.
swa start <dev-server-url>

2.4 Launch dev server to serve

You can simplify your workflow further by having the SWA CLI launch the dev server for you. Simply pass the launch command for the dev server to the --run option of swa start.

swa start <dev-server-url> --run <dev-server-launch-cmd>

For example: Here is what that lools like for a few well-known front-end technologies:

# npm start script (React)
swa start http://localhost:3000 --run "npm start"

# dotnet watch (Blazor)
swa start http://localhost:5000 --run "dotnet watch run"

# Jekyll
swa start http://localhost:4000 --run "jekyll serve"

Have a custom script that launches the dev server for you? That works too:

# custom script
swa start http://localhost:4200 --run "./"

Then access the application with the emulated services from http://localhost:4280

2.5 Default Dev Server ports

Here are some of the default ports used by dev servers in popular front-end frameworks and static site generators today.

Angular4200swa start http://localhost:4200
Blazor WebAssembly5000swa start http://localhost:5000
Gatsby8000swa start http://localhost:8000
Hugo1313swa start http://localhost:1313
Next.js3000swa start http://localhost:3000
React (Create React App)3000swa start http://localhost:3000
Svelte (sirv-cli)5000swa start http://localhost:5000
Vue8080swa start http://localhost:8080
Vite-based frameworks5173swa start http://localhost:5173