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# Inspector
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> Stability: 1 - Experimental
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The `inspector` module provides an API for interacting with the V8 inspector.
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It can be accessed using:
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```js
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const inspector = require('inspector');
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```
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## Class: inspector.Session
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The `inspector.Session` is used for dispatching messages to the V8 inspector
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back-end and receiving message responses and notifications.
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### Constructor: new inspector.Session()
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<!-- YAML
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added: v8.0.0
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-->
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Create a new instance of the `inspector.Session` class. The inspector session
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needs to be connected through [`session.connect()`][] before the messages
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can be dispatched to the inspector backend.
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`inspector.Session` is an [`EventEmitter`][] with the following events:
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### Event: 'inspectorNotification'
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<!-- YAML
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added: v8.0.0
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-->
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* {Object} The notification message object
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Emitted when any notification from the V8 Inspector is received.
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```js
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session.on('inspectorNotification', (message) => console.log(message.method));
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// Debugger.paused
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// Debugger.resumed
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```
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It is also possible to subscribe only to notifications with specific method:
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### Event: <inspector-protocol-method>
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<!-- YAML
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added: v8.0.0
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-->
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* {Object} The notification message object
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Emitted when an inspector notification is received that has its method field set
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to the `<inspector-protocol-method>` value.
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The following snippet installs a listener on the [`Debugger.paused`][]
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event, and prints the reason for program suspension whenever program
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execution is suspended (through breakpoints, for example):
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```js
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session.on('Debugger.paused', ({params}) => console.log(params.hitBreakpoints));
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// [ '/node/test/inspector/test-bindings.js:11:0' ]
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```
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### session.connect()
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<!-- YAML
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added: v8.0.0
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-->
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Connects a session to the inspector back-end. An exception will be thrown
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if there is already a connected session established either through the API or by
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a front-end connected to the Inspector WebSocket port.
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### session.post(method[, params][, callback])
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<!-- YAML
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added: v8.0.0
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-->
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* method {string}
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* params {Object}
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* callback {Function}
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Posts a message to the inspector back-end. `callback` will be notified when
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a response is received. `callback` is a function that accepts two optional
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arguments - error and message-specific result.
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```js
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session.post('Runtime.evaluate', { expression: '2 + 2' },
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(error, { result }) => console.log(result));
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// Output: { type: 'number', value: 4, description: '4' }
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```
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The latest version of the V8 inspector protocol is published on the
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[Chrome DevTools Protocol Viewer][].
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Node inspector supports all the Chrome DevTools Protocol domains declared
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by V8. Chrome DevTools Protocol domain provides an interface for interacting
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with one of the runtime agents used to inspect the application state and listen
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to the run-time events.
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### session.disconnect()
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<!-- YAML
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added: v8.0.0
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-->
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Immediately close the session. All pending message callbacks will be called
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with an error. [`session.connect()`] will need to be called to be able to send
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messages again. Reconnected session will lose all inspector state, such as
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enabled agents or configured breakpoints.
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[`session.connect()`]: #sessionconnect
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[`Debugger.paused`]: https://chromedevtools.github.io/devtools-protocol/v8/Debugger/#event-paused
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[`EventEmitter`]: events.html#events_class_eventemitter
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[Chrome DevTools Protocol Viewer]: https://chromedevtools.github.io/devtools-protocol/v8/
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