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Table of Contents

  1. Architecture
  2. Components
  3. Component Data
  4. Reducers
  5. Actions

debugger

debugger is an open source project built on top of React and Redux that functions as a standalone debugger for Firefox, Chrome, and Node. This project was created to provide a debugger that is stand-alone and does not require a specific browser tool to do debugging.

This document gives a detailed view of the components, actions, and reducers that make up the debugger project. Prior knowledge of React and Redux is suggested.

React documentation can be found here. Redux documentation can be found here.

As with most documentation related to code, this document may be out of date. The last edit date occurred on August 30, 2016. If you find issues in the documentation, please file an issue as described in the contributing guide.

Architecture

debugger is a React-Redux based application — the UI is constructed using React components. The following illustration provides a simplistic high-level view:

Application-critical objects are stored in one global state object (housed in a Redux store) that some components have access to. Many components are not aware of this state, but are passed in values to render using React properties.

In the debugger project, we also often use React’s setState to manage component local state. For example, storing the state of a tree in the sources view, or using it in the App component to remember if the file search box is being displayed (cmd->p).

When a user manipulates the UI, Redux actions are fired to collect payload data, which affects the state of the application for the given operation. Actions set a specific type of operation for the store, and dispatch the event.

Reducers handle all actions and decide the new application state based on the action type. You can think of a reducer as a set of functions that take a specific action type and the current state of the app as parameters, and returns the new state of the application.

The Store is a JavaScript object that contains and manages the state of the application. After the reducers create a new version of the state, the store will fire a re-rendering of all the components. Note that a new state is created every time — the old state is not modified.

React uses a Virtual DOM; only required changes to the actual DOM will be rendered.

Components

debugger uses React components to render portions of the application. Each component’s source code is located in the src/components folder. In this section, we will cover how the presentation pieces fit together; later, we will discuss how debugger uses Redux to wire up data to each of the components.

The top-level component is the App component; it encapsulates all other components. Presented below is an overview of the component architectural relationships:

The App component uses two SplitBox components to separate the presentation of the app into three different sections. Two Draggable components are used to allow each of the sections to be expanded or collapsed.

Source Tree View

The leftmost section of the application displays the source tree for the application being debugged. Three components are used to manage the display of this data:

  • The Sources component is aware of the Redux state and the other components are not — it passes required properties to be rendered down to the other two.

  • The SourcesTree component is primarily responsible for rendering the tree with a set of files/folders that are passed in as a property.

  • The ManagedTree component uses React local state to track which nodes have been expanded or collapsed, and which node or leaf on the tree has focus.

The Sources component encapsulates SourcesTree, and SourcesTree encapsulates ManagedTree.

Source Editor/File Search

The center portion of the application displays either the source editor or a file search entry box. If the editor is displayed, rendering is handled by three main components and one dynamic component:

  • At the top of the editor is the SourceTabs component, which is responsible for rendering tabs for every open file, and highlighting the tab of the file currently open.

  • The Editor component is responsible for rendering the text, gutters, and breakpoints for the currently selected file. debugger uses the CodeMirror npm package to do the actual rendering. The Editor component manages calls to CodeMirror.

  • Any time a breakpoint is set, the Editor creates a dynamic component called Breakpoint. The Breakpoint component is contained in the EditorBreakpoint.js file. The BreakPoint component also makes calls to CodeMirror for actual rendering of the breakpoint within the editor.

  • The last component on the page is the SourceFooter component. This component renders buttons for blackboxing and prettify source functions.

At any time, a user can search the sources for a specific string by pressing cmd->p. This will replace all of the components in the center section with a search box. The search box is rendered using the Autocomplete component.

Tools View

The rightmost section of the application is handled by many components. At the top of the component architecture is the RightSidebar component, which renders the play/pause command bar and encapsulates the Accordion component, responsible for formatting and rendering the layout, including the arrow icons and headers. This component encapsulates the Breakpoints, Frames, and Scopes component:

  • The Breakpoints component renders a list of all existing breakpoints.

  • The Frames component is responsible for rendering the current call stack when a breakpoint is reached.

  • The Scopes component is responsible for rendering the current variable scopes for the given breakpoint. It uses the ObjectInspector component to render the tree for all scopes and variables. The state of which nodes are collapsed/expanded are maintained using a ManagedTree component, in similar fashion to the SourcesTree component.

Component Data

Some components in debugger are aware of the Redux store; others are not and are just rendering passed-in properties. The Redux-aware components are connected to the Redux store using the connect() method, as illustrated by the following code:

const React = require("react");
const { connect } = require("react-redux");
const { bindActionCreators } = require("redux");
.
.
const actions = require("../actions");
.
.
.

module.exports = connect(
 state => ({
  pauseInfo: getPause(state),
  expressions: getExpressions(state)
 }),
 dispatch => bindActionCreators(actions, dispatch)
)(Expressions);

This example shows the Expressions component, which should be aware of the Redux state. We are using Redux’s connect() method to connect to the Redux store. This example is pulling in pauseInfo and Expressions from the Redux state. Finally, all of the actions in the actions folder are combined, and the contained actionCreators in each of the files are set up so the actions can be called directly from the component.

Reducers

The reducers are all located in the src/reducers folder and are all combined using Redux’s combineReducers() function. This function is executed in main.js as follows:

const reducers = require("./reducers");

.

.

const store = createStore(combineReducers(reducers));

All of the reducers are combined using the index.js file in the reducers folder. In the debugger project, each reducer has an update() function to handle actions for its slice of state.

Async-requests

The async-requests reducer creates an array that stores a unique sequence number for every promise being executed from an action. It removes the sequence number from the array when a specific promise resolves or rejects. The following image shows a snapshot of the debugger state with an active promise:

Breakpoints

The breakpoints reducer is responsible for handling breakpoint state. It adds two things to the application state—an Immutable Map of breakpoint objects, and a Boolean value for whether breakpoints are disabled.

Each breakpoint object in the map contains information like the location, the actual source file, whether the breakpoint is disabled, a unique ID, and the text for the breakpoint.

The following is an example of what the breakpoints state looks like for a selected breakpoint:

The breakpoints reducer handles several action types. The actions handled by this reducer are all fired wrapped in a promise. The status of the promise can be checked in the action object using code similar to the following:

if (action.status === "start") {

Valid values are start, done and error.

The following action types are handled:

  • ADD\_BREAKPOINT - This command adds breakpoints to the state as shown in the image above. While the promise is being fulfilled, the loading attribute is set to true and a basic breakpoint object is created. If the promise is completed, the location is updated and the loading attribute is set to false. If the promise fails, the breakpoint is deleted from the state.

  • TOGGLE\_BREAKPOINTS - Sets the value of the breakpointsDisabled attribute, and is used to disable or enable all breakpoints.

  • SET\_BREAKPOINT\_CONDITION - This action sets the condition attribute for a specific breakpoint. This functionality is currently not implemented in the UI.

  • REMOVE\_BREAKPOINT - This action actually handles disabling or removing a breakpoint. If the breakpoint is being disabled, the disabled attribute of the breakpoint is set to false. If the breakpoint is removed, it is deleted from the breakpoints state.

The breakpoints reducer additionally supplies functions to retrieve information from the breakpoints state. For example, the getBreakpointsForSource() function returns all breakpoints for a given source file. The Editor component uses this to retrieve all the breakpoints for the currently opened file.

Event-listeners

The event-listeners reducer is responsible for managing the state for the current list of DOM events that currently have listeners bound in the web application being debugged. This reducer also stores the current listeners selected for the debugger to break on. Additionally this reducer manages state that keeps track of when the event listeners are being fetched with the fetchingListeners flag.

**As of this moment the UI for this feature is not implemented. I also did not see gThreadClient created.

Pause

The pause reducer is responsible for managing state variables needed to primarily handle pause and resume conditions in the debugger. These pause conditions can occur because of a set breakpoint in code being debugged, an exception, or an event listener being debugged.

  • The pause object stores information like why the debugger paused, the current call stack frame, the current source location, and the current variable scope.

  • The frames object stores all the frames for the current call stack.

  • The selectedFrame object stores the call stack frame currently selected in the debugger UI.

  • The loadedObjects object stores the currently selected and expanded variables in the scopes pane.

**The expressions object stores all of the current watch expressions, which is not implemented in the UI yet.

The pause reducer handles the following action types:

  • PAUSE – Handles loading and updating the state for all the variables described above.

  • RESUME – Clears all state variables associated with a pause.

  • BREAK\_ON\_NEXT – This action type is triggered when a user presses the pause button and informs the JavaScript engine to break on the next JavaScript statement. Until the engine actually breaks, a flag that tracks the status is stored in state.

  • LOADED\_FRAMES – This action type occurs when all the frames for the call stack have been retrieved. As stated above, these are stored in the application state.

  • SELECT\_FRAME - This action type occurs when a user is selecting different frames of the call stack while the debugger is paused.

  • LOAD\_OBJECT\_PROPERTIES – This action type occurs when a user is expanding the variable tree under the scope pane. The currently expanded variable is then stored in state.

  • PAUSE\_ON\_EXCEPTIONS – This action type occurs when the settings (pause on exceptions and ignore caught exceptions) for the debugger are changed. These values are then stored in state.

  • ADD\_EXPRESSION – This action type occurs when a new watch expression has been added.

  • EVALUATE\_EXPRESSION – This action type is triggered when a watch expression is being evaluated.

  • UPDATE\_EXPRESSION – This action type is triggered when updating a watch expression.

  • DELETE\_EXPRESSION – This action type is triggered when a watch expression is deleted.

The pause reducer also has many getter functions to retrieve portions of state that are stored by this reducer.

Sources

The sources reducer is responsible for maintaining state variables that are used in the managing of opening and closing source files in the debugger. The state variables for this reducer contain elements that manage things like sources in the source tree, the currently open file, the source text for all open files, source maps for source files, and open tabs within the editor.

  • The sources object contains an array of all the sources in the source tree and is built when a project is loaded into the debugger. When the "Prettify Source" button is selected, a new source is added to the sources object representing the new text prettified.

  • The selectedSource object contains information on the currently opened file in the editor, and is altered when new files are opened or tabs are switched.

  • The sourcesText state variable is an array of objects where each object contains the source text for an open file in the debugger.

  • The sourceMaps object is similar to sourcesText, but it contains the associated source map text.

  • The tabs object manages how many tabs are opened, and what file is associated with each.

The sources reducer handles the following action types:

  • ADD\_SOURCE – This action type occurs when a project is loading and source files are being added to the source tree. Additionally, "Prettify Source" will add additional files.

  • ADD\_SOURCES – This type is similar to ADD\_SOURCE, but takes a map of source files. Currently, this type is not used in the debugger.

  • LOAD\_SOURCE\_MAP – This action type occurs when a source map is loaded for a specific source file.

  • SELECT\_SOURCE – This action type is triggered when a file is opened, or a different tab is selected in the debugger.

  • SELECT\_SOURCE\_URL – This action type is triggered when a URL designates the selected source file. Need more data on this one.

  • CLOSE\_TAB – This action type is triggered when a tab is closed in the debugger. The tab is cleared from state and the proper source is selected.

  • LOAD\_SOURCE\_TEXT – This event is triggered when the text of a file is being loaded. The event is wrapped in a promise, so it will be called twice — once when it is started, and once when it is complete. Once loaded, the text is loaded in the sourcesText state object.

  • BLACKBOX – This event is triggered when blackboxing is enabled and the button is selected for a given source. The blackbox status for each file is stored in the source's state object.

  • TOGGLE\_PRETTY\_PRINT – The event is triggered when a toggling of the "Prettify Source" button is selected. The reducer updates the sourcesText with the new text, and updates the isPrettyPrinted flag in the sources state object.

The sources reducer also has many getter functions to retrieve portions of state that are handled in this reducer.

Tabs

The tabs reducer is used to track which connected application is being debugged. When the main debugger is started, every connected application will be displayed. For example, all the open tabs in a Firefox browser that are connected to the debugger will be shown.

This reducer stores two objects in state:

  • The tabs object stores an array of connected applications.

  • The selectedTab object stores the current application that is being debugged.

The tabs reducer handles the following action types:

  • ADD\_TABS – This action type is triggered for every connected application when the debugger is started.

  • SELECT\_TAB – This action type is triggered when a specific application is selected for debugging.

Actions

The actions in debugger are all located in the src/actions folder; there is an action file corresponding to each reducer, which is responsible for dispatching the proper event when the application state needs to be modified. In this section, we will cover each action file. As stated earlier, many of the actions defined in these files are actionCreators that are setup to use in a component via the bindActionsCreator() Redux method.

breakpoints

The breakpoints action file handles manipulating breakpoints in the debugger.

The breakpoints file exports the following functions:

  • enableBreakpoint() - This function dispatches the ADD\_BREAKPOINT action, and is called from the breakpoints component when a user selects the checkbox next to a breakpoint listed in the "Breakpoints" category on the right bar. Breakpoints listed here are currently enabled, or previously enabled and now disabled, therefore this function is only called when re-enabling an existing breakpoint.

  • addBreakpoint() - This function dispatches the ADD\_BREAKPOINT action and is called from the Editor component when a user clicks on the left gutter next to the source text and no breakpoint is currently on this line.

  • disableBreakpoint - This function dispatches the REMOVE\_BREAKPOINT action, and is called from the Breakpoints component when clicking on the checkbox next to a breakpoint listed in the right bar under the "Breakpoints" category. Ultimately, the breakpoint is not removed; the disabled flag is set for the specific breakpoint, which is handled in the breakpoints reducer.

  • removeBreakpoint() - This function dispatches the REMOVE\_BREAKPOINT action and is called from the Editor component when a user clicks on an existing breakpoint from the left side gutter.

  • toggleAllBreakpoints() – This function dispatches the TOGGLE\_BREAKPOINTS action and is called from the RightSideBar component when the "Disable/Enable All Breakpoints" button is clicked. This results in either disableBreakpoint() or enableBreakpoint() being called for every breakpoint currently active.

  • setBreakpointCondition() – Currently not implemented.

event-listeners

The event-listeners action file handles retrieving a list of all the DOM events that currently have listeners bound in the web application being debugged. In addition, it handles selecting specific ones for the debugger to break on.

The event-listeners file exports the following functions:

  • updateEventBreakpoints() – This function passes an array of DOM events that should cause the debugger to break to the connected client being debugged. Next, it dispatches the UPDATE\_EVENT\_BREAKPOINTS action. The UI is not yet built for this.

  • fetchEventListeners() – This function retrieves a list of DOM events that currently have listeners bound for the application being debugged. Once retrieved, the fetchEventListeners() function dispatches the FETCH\_EVENT\_LISTENERS action.

pause

The pause action file handles all functions responsible for pausing, resuming, and manipulating the debugger by stepping through code. The functions contained in this file handle several calls back and forth with the connected client (i.e. Firefox, Chrome, or Node). Most of the client functions are defined in the src/clients/specificclient/events.js and src/clients/specificclient/commands.js files.

The pause action file exports the following functions:

  • addExpression() – Called from the Expressions component, this function dispatches the ADD\_EXPRESSION action. Expressions are passed and evaluated by the connected client.

  • updateExpression() - Called from the Expressions component, this function dispatches the UPDATE\_EXPRESSION action. Expressions are passed and evaluated by the connected client.

  • deleteExpression() - Called from the Expressions component, this function dispatches the DELETE\_EXPRESSION action. Expressions are passed and evaluated by the connected client.

  • resumed() – Called from the connected client, this function dispatches the RESUME action. This function is called anytime the connected client resumes execution after a pause. This includes using a step function to advance execution by one line.

  • paused() – Called from the connected client anytime the client pauses and dispatches a PAUSED action. Before dispatching, the call stack frames, current frame, and reason for the pause are all retrieved from the connected client. These values are all passed in the dispatched action.

  • pauseOnExceptions() – This function is called from the RightSideBar component and dispatches the PAUSE\_ON\_EXCEPTIONS action. Before doing this, the connected client is called and passes two values to instruct the connected client to pause/not pause on exceptions, and whether to ignore caught exceptions.

  • command() – This function is called indirectly by the RightSideBar component. This is a generic function that sends different commands to the connected client. After the command is executed, the COMMAND action is dispatched. The client commands are defined in the src/clients/specificclient/commands.js file.

  • stepIn() – This function is called from the RightSideBar. This function calls the command() function to pass it to the connected client.

  • stepOut() - This function is called from the RightSideBar. This function calls the command() function to pass it to the connected client.

  • stepOver() - This function is called from the RightSideBar. This function calls the command() function to pass it to the connected client.

  • resume() – This function is called from the RightSideBar when the play button is pressed and the debugger is currently paused. This function calls the command() function to pass it to the connected client.

  • breakOnNext() – This function is called from the RightSideBar when the pause button is pressed and the debugger is currently not paused. This function calls the connected clients breakOnNext() function, which is defined in the src/clients/specificclient/commands.js file. After returning from the client call the BREAK\_ON\_NEXT action is dispatched.

  • selectFrame() – This function is called from the Frames component when a user selects a specific frame under the call stack UI. This function first calls the selectLocation() function, which is defined in the sources action. This loads up the editor with text for the specific frame. The SELECT\_FRAME action is then dispatched.

  • setPopupObjectProperties() – This function is called from the Popup component, which then use this data to pass all the properties from the hovered variable as root nodes of the ObjectInspector component. The function dispatches the SET\_POPUP\_OBJECT\_PROPERTIES action.

sources

The sources action is responsible for providing functions that support opening files in the editor, managing the tabs within the editor, and supplying blackbox and pretty-print functionality. The sources action file exports the following functions:

  • newSource() – This function is called from the connected client as defined in src/clients/specificclient/events.js when a project is loaded. In addition, newSource() is called whenever a source map is loaded to add it to the project. This function checks to see if a source map needs to be loaded and if so dispatches the LOAD\_SOURCE\_MAP action, then the ADD\_SOURCE action. Finally, if this source is to be displayed in the editor, the selectLocation() function is called.

  • selectLocation() – This function is called any place in the UI where a specific source needs to be displayed in the editor. This can happen from the source tree, the tabs across the top of the editor, in the Call Stack panel, and when the "Prettify Source" button is pressed. These locations correspond to the SourcesTree, SourceTabs, Breakpoints, and SourceFooter components. The function first dispatches the LOAD\_SOURCE\_TEXT action, which is wrapped in a promise. The SELECT\_SOURCE action is then dispatched. This usually results in a LOAD\_SOURCE\_TEXT action firing first, then the SELECT\_SOURCE action, followed by another LOAD\_SOURCE\_TEXT action once the promise completes and the text is loaded.

  • selectSourceURL() – Currently this function is only exposed in the src/main.js file to external clients. The function first dispatches a SELECT\_SOURCE action, and then dispatches the SELECT\_SOURCE\_URL action. As stated above, the text is loaded with the selectLocation() function.

  • closeTab() – This function is called from the SourceTabs() component whenever a tab is closed. The function dispatches the CLOSE\_TAB action.

  • blackbox() – This function is called from the SourceFooter component whenever the blackbox button is pressed. The button acts as a toggle for the file currently open in the editor. The function dispatches the blackbox action and calls the connected client to either enable or disable blackboxing on a specific file.

  • togglePrettyPrint() - This function is called from the SourceFooter component whenever the "Prettify Source" button is pressed. This function first creates a new URL for the formatted text, and then dispatches an ADD\_SOURCE action through an internal function, which adds the new file to the project. Next, the function dispatches a TOGGLE\_PRETTY\_PRINT action, which contains a promise that starts a Worker thread to transform the source. The worker is defined in assets/build/pretty-print-worker.js. The selectLocation() function is then called to select the new source.

  • loadSourceText() – This function is called whenever a source is selected using the selectLocation() function (described above), and whenever getTextForSources() is called (described below). The loadSourceText() function is responsible for loading the source text for an individual file. The function first checks to see if the text for the selected file is already stored in the state. If it is, the function returns this text. If the text is not already stored, the LOAD\_SOURCE\_TEXT action is dispatched and is wrapped in a promise. This function will dispatch the LOAD\_SOURCE\_TEXT once for the start of the promise, and once for when it completes. It returns the source text and, if a source map is used, the text for the source map will also be returned. These are then stored in state by the reducer.

  • getTextForSources() – This function takes a set of source files and calls loadSourceText() to load each file. Currently this function is not used in debugger.

tabs

The tabs action is responsible for gathering all connected clients that can be debugged, and gathering the tabs for each application that can be debugged on the connected client. The tabs action file exports the following functions:

  • newTabs() – This function is called from src/main.js and sets the action type to ADD\_TABS. The action is dispatched from the src/main.js when debugger is loading and displaying the main page, or when starting to debug when a specific tab is selected.

  • selectTab() – This function is called from src/main.js when a user has selected a specific tab from a connected application to debug. It sets the action type to SELECT\_TAB and the action is then dispatched in src/main.js.