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Hot Module Replacement

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If Hot Module Replacement has been enabled via the HotModuleReplacementPlugin, its interface will be exposed under the module.hot property. Typically, users will check to see if the interface is accessible, then begin working with it. As an example, here's how you might accept an updated module:

if (module.hot) {
  module.hot.accept('./library.js', function() {
    // Do something with the updated library module...
  })
}

The following methods are supported...

accept

Accept updates for the given dependencies and fire a callback to react to those updates.

module.hot.accept(
  dependencies, // Either a string or an array of strings
  callback // Function to fire when the dependencies are updated
)

decline

Reject updates for the given dependencies forcing the update to fail with a 'decline' code.

module.hot.decline(
  dependencies // Either a string or an array of strings
)

dispose (or addDisposeHandler)

Add a handler which is executed when the current module code is replaced. This should be used to remove any persistent resource you have claimed or created. If you want to transfer state to the updated module, add it to given data parameter. This object will be available at module.hot.data after the update.

module.hot.dispose(data => {
  // Clean up and pass data to the updated module...
})

removeDisposeHandler

Remove the callback added via dispose or addDisposeHandler.

module.hot.removeDisposeHandler(callback)

status

Retrieve the current status of the hot module replacement process.

module.hot.status() // Will return one of the following strings...
Status
Description
Status
idle
Description
The process is waiting for a call to check (see below)
Status
check
Description
The process is checking for updates
Status
prepare
Description
The process is getting ready for the update (e.g. downloading the updated module)
Status
ready
Description
The update is prepared and available
Status
dispose
Description
The process is calling the dispose handlers on the modules that will be replaced
Status
apply
Description
The process is calling the accept handlers and re-executing self-accepted modules
Status
abort
Description
An update was aborted, but the system is still in it's previous state
Status
fail
Description
An update has thrown an exception and the system's state has been compromised

check

Test all loaded modules for updates and, if updates exist, apply them.

module.hot.check(autoApply).then(outdatedModules => {
  // outdated modules...
}).catch(error => {
  // catch errors
});

The autoApply parameter can either be a boolean or options to pass to the apply method when called.

apply

Continue the update process (as long as module.hot.status() === 'ready').

module.hot.apply(options).then(outdatedModules => {
  // outdated modules...
}).catch(error => {
  // catch errors
});

The optional options object can include the following properties:

  • ignoreUnaccepted (boolean): Ignore changes made to unaccepted modules.
  • ignoreDeclined (boolean): Ignore changes made to declined modules.
  • ignoreErrored (boolean): Ignore errors throw in accept handlers, error handlers and while reevaluating module.
  • onDeclined (function(info)): Notifier for declined modules
  • onUnaccepted (function(info)): Notifier for unaccepted modules
  • onAccepted (function(info)): Notifier for accepted modules
  • onDisposed (function(info)): Notifier for disposed modules
  • onErrored (function(info)): Notifier for errors

The info parameter will be an object containing some of the following values:

{
  type: "self-declined" | "declined" | 
        "unaccepted" | "accepted" | 
        "disposed" | "accept-errored" | 
        "self-accept-errored" | "self-accept-error-handler-errored",
  moduleId: 4, // The module in question.
  dependencyId: 3, // For errors: the module id owning the accept handler.
  chain: [1, 2, 3, 4], // For declined/accepted/unaccepted: the chain from where the update was propagated.
  parentId: 5, // For declined: the module id of the declining parent
  outdatedModules: [1, 2, 3, 4], // For accepted: the modules that are outdated and will be disposed
  outdatedDependencies: { // For accepted: The location of accept handlers that will handle the update
    5: [4]
  },
  error: new Error(...), // For errors: the thrown error
  originalError: new Error(...) // For self-accept-error-handler-errored: 
                                // the error thrown by the module before the error handler tried to handle it.
}

addStatusHandler

Register a function to listen for changes in status.

module.hot.addStatusHandler(status => {
  // React to the current status...
})

removeStatusHandler

Remove a registered status handler.

module.hot.removeStatusHandler(callback)

Further Reading

Contributors

skipjack sokra tbroadley