TypeScript Command Pattern example for CLJS: <https://groups.google.com/forum/#!topic/comp.lang.javascript/N8jA1Blh9LY>

Maze.ts

abstract class Command {
    abstract execute(): void
}

abstract class UndoableCommand extends Command {
    abstract undo(): void
}

class Direction {
    static readonly UP = 0
    static readonly RIGHT = 90
    static readonly DOWN = 180
    static readonly LEFT = 270

    constructor(readonly angle: number) { }

    // ... other methods ellided for clarity

    opposite(): Direction {
        return new Direction((this.angle + 180) % 360)
    }
}

/**
 * A class representing a Maze game
 * where your moves can be undone
 */
class Maze {
    // A "stack" of commands for history tracking
    protected _commands: Command[]

    //... methods for defining maze parts and rendering ellided for clarity

    move(direction: Direction): void {
        // ellided for clarity
    }

    protected _doCommand(command: Command) {
        if (command) {
            this._commands.push(command)
            command.execute()
        }
    }

    protected _undoCommand() {
        if (this._commands.length) {
            let top = this._commands[this._commands.length - 1]
            if (top instanceof UndoableCommand) {
                this._commands.pop()
                top.undo()
            }
        }
    }
}

// Define an undoable command

class MazeMove extends UndoableCommand {
    constructor(
        readonly maze: Maze,
        readonly direction: Direction
    ) { super() }

    execute(): void {
        this.maze.move(this.direction)
    }

    undo(): void {
        this.maze.move(this.direction.opposite())
    }
}