# Hot Reload

To speed the development cycles, es4x supports simple hot-reload. The functionality is very basic. On a file change, the application will be stopped abruptly and restarted. This feature is not es4x specific, in fact it just relies on vertx core functionality.

# Walk-through

Imagine the following application composed from 4 source js files:

  1. index.js
  2. m/a.js
  3. m/b.js
  4. m/c.js

The content of these files is as follows:

# index.js

const a = require('./m/a');

Call a function defined on a relative module a.

# m/a.js

const b = require('./b');

function a() {
    print('Hello from A');

module.exports = a;

Prints a message and calls another module b.

# m/b.js

const c = require('./c');

// changed B
function b() {
print('Hello from B');

module.exports = b;

Prints a message and calls another module c.

# m/c.js

function c() {
    print('Hello from C');

module.exports = c;

Prints the final message.

# Running

In order to run an application with hot-reload all you need is to use the vert.x redeploy command.

In this example one would execute:

es4x run --redeploy "m/*" index.js

It is important to know that the redeploy watch list works with files, so in order to watch a directory, one needs to watch a wildcard.

$ ./node_modules/.bin/es4x --redeploy "m/*"
Watched paths: [/home/hello/./m]
Starting the vert.x application in redeploy mode
Starting vert.x application...
Hello from A
Hello from B
Hello from C
Succeeded in deploying verticle

When any of the files under m are touched you will see a similar message in the console:

Stopping vert.x application 'ec467de2-ca71-43c6-98d8-9da0cc0d24f8-redeploy'
Application 'ec467de2-ca71-43c6-98d8-9da0cc0d24f8-redeploy' terminated with status 0
Starting vert.x application...
Redeployment done in 66 ms.
Hello from A
Hello from B
Hello from C
Succeeded in deploying verticle

This will happen for each file you touch.

# Running a task before redeploy

While re-deploy is already a time saver, there are usually steps required to be executed before the re-deploy happens. For example a build step, like compile typescript to javascript, by running tsc. For this we can run the application as:

es4x run --redeploy "m/*" --on-redeploy "tsc" index.js

For more information read the all the options on the run command:

es4x run --help