The GUI control provides a drop-down menu with multiple types of items. The current set of items is:

• slider: Select a numeric value
• chooser: Select a text value among a list
• switch: Switch between two values via a boolean value
• button: Execute a command
• color: Choose a color mongst a colors pop-up
• monitor: Follow of the progress of an object and one of it's properties
• input: Enter text to be used by the item

The API for these is a key-object pair:

• The text label for the item and
• An object with the item name with it's available values, and a command that is executed when the item is chosen. Here's an example of each type:

const gui = new GUI({
    turtlesSize: {
        slider: [1, [0.5, 10, 0.5]],
        cmd: val => (view.drawOptions.turtlesSize = val),
    },
    turtlesShape: {
        chooser: ['bug', ['bug', 'dart', 'person', 'circle', 'arrow']],
        cmd: val => (view.drawOptions.turtlesShape = val),
    },
    useMouse: {
        switch: false,
        cmd: val => {
            if (val) {
                mouse.start()
            } else {
                mouse.stop()
            }
        },
    },
    downloadCanvas: {
        button: () => view.downloadCanvas(),
    },
    turtlesColor: {
        color: '#ff0000',
        cmd: val => (view.drawOptions.turtlesColor = val),
    },
    modelTicks: {
        monitor: [model, 'ticks'],
    },
    setTitle: {
        input: 'Play',
        cmd: val => (document.title = val),
    },
})

This would result in this menu:

Here is an example using each one of them.

Finally, there is the ability to "nest" GUI items in folders.

Here is an example, a Turtles Folder. Click on the Folder to expand it.

Folders are created like this:

'Turtles Folder': {
    turtlesShape: {
        chooser: ['bug', ['bug', 'dart', 'person', 'circle', 'arrow']],
        cmd: val => view.drawOptions.turtlesShape = val,
    },
    turtlesSize: {
        slider: [1, [0.5, 10, 0.5]],
        cmd: val => view.drawOptions.turtlesSize = val,
    },
    turtlesColor: {
        color: '#ff0000',
        cmd: val => view.drawOptions.turtlesColor = val,
    },
},