Table of Contents

Converting Keybinding Definitions to Actions

This module defines the schema of the configuration file using TypeScript interfaces. We parse the configuration JSON to TypeScript objects which directly define all the valid keyboard sequences and the commands that these will invoke.

action.ts imports
import * as vscode from 'vscode'

Action Definitions

The keybinding configuration consist of actions that can take three forms: an action can be a command (defined later), a keymap, or a number that refers to a keymap defined earlier.

export type Action = Command | Keymap | number

Commands can be invoked in four ways: by specifying just command a name (string), or using a conditional command, a command with parameters, or a sequence (array) of commands. The definition is recursive, meaning that a sequence can contain all four types of commands.

export type Command = string | Conditional | Parameterized | Command[]

A conditional command consist of condition (a JavaScript expression) and set of branches to take depending on the result of the condition. Each branch can be any type of command defined above.

export interface Conditional {
    condition: string
    [branch: string]: Command

A command that takes arguments can be specified using the Parameterized interface. Arguments can be given either as an object or a string, which is assumed to contain a valid JS expression. Additionally, you can specify that the command is run multiple times by setting the repeat property. The property must be either a number, or a JS expression that evaluates to a number. If it evaluates to some other type, the expression is used as a condition that is evaluated after the command is run. If the expression returns a truthy value, the command is repeated.

export interface Parameterized {
    command: string
    args?: {} | string
    repeat?: number | string

A keymap is a dictionary of keys (characters) to actions. Keys are either single characters or character ranges, denoted by sequences of <char>,<char> and <char>-<char>. Values of the dictionary can be also nested keymaps. This is how you can define commands that require multiple keypresses.

keymap example When the value of a key is number, it refers to another keymap whose id equals the number. The number can also point to the same keymap where it resides. With this mechanism, you can define recursive keymaps that can take (theoretically) infinitely long key sequences. The picture on the right illustrates this.

The help field contains help text that is shown in the status bar when the keymap is active.

export interface Keymap {
    id: number
    help: string
    [key: string]: Action

Cursor Shapes

You can use various cursor shapes in different modes. The list of available shapes is defined below.

type Cursor =
    | "block"
    | "block-outline"
    | "line"
    | "line-thin"
    | "underline"
    | "underline-thin"
    | undefined

Configuration State

The variables below contain the current cursor configuration.

let insertCursorStyle: vscode.TextEditorCursorStyle
let normalCursorStyle: vscode.TextEditorCursorStyle
let searchCursorStyle: vscode.TextEditorCursorStyle

Another thing you can set in config, is whether ModalEdit starts in normal mode.

let startInNormalMode: boolean

The root of the action configuration is keymap. This defines what key sequences will be run when keys are pressed in normal mode.

let baseKeymap: Keymap
let selectKeymap: Keymap

The current active keymap is stored here. The active keymap changes when the user invokes a multi-key action sequence.

let currentKeymap: Keymap | null = null

The last command run is also stored. This is needed to run commands which capture the keyboard.

let lastCommand: string

The key sequence that user has pressed is stored for error reporting purposes and to make it available to command arguments.

let keySequence: string[] = []

We need a dictionary that returns a keymap for given id.

let keymapsById: { [id: number]: Keymap }

Configuration Accessors

The following functions return the current configuration settings.

export function getInsertCursorStyle(): vscode.TextEditorCursorStyle {
    return insertCursorStyle

export function getNormalCursorStyle(): vscode.TextEditorCursorStyle {
    return normalCursorStyle

export function getSearchCursorType(): vscode.TextEditorCursorStyle {
    return searchCursorStyle

export function getStartInNormalMode(): boolean {
    return startInNormalMode

You can also set the last command from outside the module.

export function setLastCommand(command: string) {
    lastCommand = command


To enable logging and error reporting ModalEdit creates an output channel that is visible in the output pane. The channel is created in the extension activation hook, but it is passed to this module using the setOutputChannel function.

let outputChannel: vscode.OutputChannel

export function setOutputChannel(channel: vscode.OutputChannel) {
    outputChannel = channel

Once the channel is set, we can output messages to it using the log function.

export function log(message: string) {

Updating Configuration from settings.json

Whenever you save the user-level settings.json or the one located in the .vsode directory VS Code calls this function that updates the current configuration.

export function updateFromConfig(): void {
    const config = vscode.workspace.getConfiguration("modaledit")
    insertCursorStyle = toVSCursorStyle(
        config.get<Cursor>("insertCursorStyle", "line"))
    normalCursorStyle = toVSCursorStyle(
        config.get<Cursor>("normalCursorStyle", "block"))
    searchCursorStyle = toVSCursorStyle(
        config.get<Cursor>("searchCursorStyle", "underline"))
    startInNormalMode = config.get<boolean>("startInNormalMode", true)

The following function updates base keymap and select-mode keymap.

function UpdateKeybindings(config: vscode.WorkspaceConfiguration) {
    log("Validating keybindings in 'settings.json'...")
    keymapsById = {}
    errors = 0
    let sel = config.get<object>("selectbindings")
    if (isKeymap(sel)) {
        selectKeymap = sel
    let base = config.get<object>("keybindings")
    if (isKeymap(base)) {
        baseKeymap = base
        log("ERROR: Invalid configuration structure. Keybindings not updated.")
    if (errors > 0)
        log(`Found ${errors} error${errors > 1 ? "s" : ""}. ` +
            "Keybindings might not work correctly.")
        log("Validation completed successfully.")

To make sure that the keybinding section is valid, we define a function that checks it. At the same time the function resolves all the keymaps that are referred by an id. It records the number of errors.

let errors: number

The keymap ranges are recognized with the following regular expression. Examples of valid key sequences include:

  • 0-9
  • a,b,c
  • d,e-h,l

Basically you can add individual characters to the range with a comma , and an ASCII range with dash -. The ASCII code of the first character must be smaller than the second one's.

let keyRE = /^.([\-,].)+$/

The function itself is recursive; it calls itself, if it finds a nested keymap. It stores all the keymaps it encounters in the keymapsById dictionary.

function validateAndResolveKeymaps(keybindings: Keymap) {
    function error(message: string) {
        log("ERROR: " + message)
    if (typeof === 'number')
        keymapsById[] = keybindings
    for (let key in keybindings) {
        if (keybindings.hasOwnProperty(key) && key != "id" && key != "help") {
            let target = keybindings[key]
            if (isKeymap(target))
            else if (typeof target === 'number') {
                let id = target
                target = keymapsById[id]
                if (!target)
                    error(`Undefined keymap id: ${id}`)
                    keybindings[key] = target
            if (key.match(keyRE))
                for (let i = 1; i < key.length; i += 2) {
                    if (key[i] == '-') {
                        let first = key.charCodeAt(i - 1)
                        let last = key.charCodeAt(i + 1)
                        if (first > last)
                            error(`Invalid key range: "${key}"`)
                            for (let i = first; i <= last; i++)
                                keybindings[String.fromCharCode(i)] = target
                    else {
                        keybindings[key[i - 1]] = target
                        keybindings[key[i + 1]] = target
            else if (key.length != 1)
                error(`Invalid key binding: "${key}"`)

The helper function below converts cursor styles specified in configuration to enumeration members used by VS Code.

function toVSCursorStyle(cursor: Cursor): vscode.TextEditorCursorStyle {
    switch (cursor) {
        case "line": return vscode.TextEditorCursorStyle.Line
        case "block": return vscode.TextEditorCursorStyle.Block
        case "underline": return vscode.TextEditorCursorStyle.Underline
        case "line-thin": return vscode.TextEditorCursorStyle.LineThin
        case "block-outline": return vscode.TextEditorCursorStyle.BlockOutline
        case "underline-thin": return vscode.TextEditorCursorStyle.UnderlineThin
        default: return vscode.TextEditorCursorStyle.Line

Type Predicates

Since JavaScript does not have dynamic type information we need to write functions that check which type of action we get from the configuration. First we define a high-level type predicate that checks if a value is an action.

function isAction(x: any): x is Action {
    return isCommand(x) || isKeymap(x) || isNumber(x)

This one checks whether a value is a string.

function isString(x: any): x is string {
    return x && typeof x === "string"

This one checks whether a value is a number.

function isNumber(x: any): x is number {
    return x && typeof x === "number"

This one identifies an object.

function isObject(x: any): boolean {
    return x && typeof x === "object"

This checks if a value is a command.

function isCommand(x: any): x is Action {
    return isString(x) || isParameterized(x) || isConditional(x) ||

This checks if a value is an array of commands.

function isCommandSequence(x: any): x is Command[] {
    return Array.isArray(x) && x.every(isCommand)

This recognizes a conditional action.

function isConditional(x: any): x is Conditional {
    return isObject(x) && isString(x.condition) &&
        Object.keys(x).every(key =>
            key === "condition" || isCommand(x[key]))

This asserts that a value is a parameterized command.

function isParameterized(x: any): x is Parameterized {
    return isObject(x) && isString(x.command) &&
        (!x.args || isObject(x.args) || isString(x.args)) &&
        (!x.repeat || isNumber(x.repeat) || isString(x.repeat))

And finally this one checks if a value is a keymap.

function isKeymap(x: any): x is Keymap {
    return isObject(x) && !isConditional(x) && !isParameterized(x) &&

Executing Commands

In the end all keybindings will invoke one or more VS Code commands. The following function runs a command whose name and arguments are given as parameters. If the command throws an exception because of invalid arguments, for example, the error is shown in the popup window at the corner of the screen.

async function executeVSCommand(command: string, any[]): Promise<void> {
    try {
        await vscode.commands.executeCommand(command,
        lastCommand = command
    catch (error) {

evalString function evaluates JavaScript expressions. Before doing so, it defines some variables that can be used in the evaluated text.

function evalString(str: string, __selecting: boolean): any {
    let __file = undefined
    let __line = undefined
    let __col = undefined
    let __char = undefined
    let __selection = undefined
    let __keySequence = keySequence
    let __keys = keySequence
    let __rkeys = keySequence.slice().reverse()
    let editor = vscode.window.activeTextEditor
    if (editor) {
        let cursor =
        __file = editor.document.fileName
        __line = cursor.line
        __col = cursor.character
        __char = editor.document.getText(new vscode.Range(cursor,
            cursor.translate({ characterDelta: 1 })))
        __selection = editor.document.getText(editor.selection)
    try {
        return eval(`(${str})`)
    catch (error) {
        vscode.window.showErrorMessage("Evaluation error: " + error.message)

We need the evaluation function when executing conditional command. The condition is evaluated and if a key is found that matches the result, it is executed.

async function executeConditional(cond: Conditional, selecting: boolean):
    Promise<void> {
    let res = evalString(cond.condition, selecting)
    let branch = isString(res) ? res : JSON.stringify(res)
    if (branch && isAction(cond[branch]))
        await execute(cond[branch], selecting)

Parameterized commands can get their arguments in two forms: as a string that is evaluated to get the actual arguments, or as an object. Before executing the command, we inspect the repeat property. If it is string we evaluate it, and check if the result is a number. If so, we update the repeat variable that designates repetition count. If not, we treate it as a continue condition. The subroutine exec runs the command either repeat times or as long as the expression in the repeat property returns a truthy value.

async function executeParameterized(action: Parameterized, selecting: boolean) {
    let repeat: string | number = 1
    async function exec(args?: any) {
        let cont = true
        if (isString(repeat))
            do {
                await executeVSCommand(action.command, args)
                cont = evalString(repeat, selecting)
            while (cont)
            for (let i = 0; i < repeat; i++)
                await executeVSCommand(action.command, args)
    if (action.repeat) {
        if (isString(action.repeat)) {
            let val = evalString(action.repeat, selecting)
            if (typeof val === 'number')
                repeat = Math.max(1, val)
                repeat = action.repeat
            repeat = Math.max(1, action.repeat)
    if (action.args) {
        if (typeof action.args === 'string')
            await exec(evalString(action.args, selecting))
            await exec(action.args)
        await exec()

Executing Actions

Before running any commands, we need to identify which type of action we got. Depending on the type we use different function to execute the command. If the action is not a command, it has to be a keymap. Since we resolved id referenences in validateAndResolveKeymaps, an action has to be a keymap object at this point. We set the new keymap as the active one.

async function execute(action: Action, selecting: boolean): Promise<void> {
    currentKeymap = null
    if (isString(action))
        await executeVSCommand(action)
    else if (isCommandSequence(action))
        for (const command of action)
            await execute(command, selecting)
    else if (isConditional(action))
        await executeConditional(action, selecting)
    else if (isParameterized(action))
        await executeParameterized(action, selecting)
        currentKeymap = <Keymap>action

Key Press Handler

Now that the plumbing of actions is implemented, it is straightforward to map the pressed key to an action. The special case occurs when a command captures the keyboard. Then we rerun the previous command and give the key to it as an argument.

Otherwise we just check if the current keymap contains binding for the key pressed, and execute the action. If not, we present an error to the user.

As a last step the function returns true, if the current keymap is null. This indicates that the key invoked a command instead of just changing the active keymap.

export async function handleKey(key: string, selecting: boolean,
    capture: boolean, userInitiated: boolean): Promise<boolean> {

    function error() {
        vscode.window.showWarningMessage("ModalEdit: Undefined key binding: " +
            keySequence.join(" - "))
        currentKeymap = null

    if (userInitiated)
    if (capture && lastCommand)
        executeVSCommand(lastCommand, key)
    else if (currentKeymap) {
        if (currentKeymap[key])
            await execute(currentKeymap[key], selecting)
    else {
        if (selecting && selectKeymap[key])
            await execute(selectKeymap[key], selecting)
        else if (baseKeymap[key])
            await execute(baseKeymap[key], selecting)
    if (!currentKeymap && userInitiated)
        keySequence = []
    return !currentKeymap

Keymap Help

When defining complex key sequences you can help the user by defining what keys she can press next and what they do. If the help is defined, it is shown in the status bar.

export function getHelp(): string | undefined {
    return currentKeymap?.help