The simplest way to save your parameters is via DAT.GUI.saveURL(). This method directs your browser to a URL containing the current GUI settings.

// Make a button for the url function
gui.add(DAT.GUI, "saveURL");

Let's say you'd like to share your settings with someone. Instead of sending a long link with lots of parameters stored in it, you can make your saved settings the defaults.

First, add the method DAT.GUI.showSaveString() to a gui object:

var gui = new DAT.GUI();

// Add some stuff (and pretend I change their values);
gui.add(someObject, "someProperty");
gui.add(someObject, "someOtherProperty");

// Make a save button.
gui.add(DAT.GUI, "showSaveString");

Clicking the "showSaveString" button bring up an alert with a string. Copy and paste that string into the method DAT.GUI.load() before you instantiate any gui objects.

// Replace COPIED STRING with the value you got from showSaveString()
DAT.GUI.load("COPIED STRING");

var gui = new DAT.GUI();

// Now these properties will be set to the values you just saved.
gui.add(someObject, "someProperty");
gui.add(someObject, "someOtherProperty");

Save strings won't work if you change the order in which you've added properties to your gui objects, or the order of the gui objects themselves.. If you want to add more parameters to your gui and use an old save string, make sure they're added after the properties whose values you've saved.

gui.add(obj, "propertyName").options(1, 2, 3, 5, 8);

// Alternatively, you can specify custom labels using object syntax
gui.add(obj, "propertyName").options({'Small': 1, 'Medium': 2, 'Large': 3});

To fire a function whenever a user changes a variable via the GUI, use the following syntax:

gui.add(obj, "propertyName").onChange(function(newValue) {
   alert("You changed me to " + newValue);
});

This can be slightly annoying for types like number or string. You may not want to fire a function while the user is sliding, or while they're typing. To fire a function when the user has finished making changes, use the following:

gui.add(obj, "propertyName").onFinishChange(function(newValue) {
   alert("You just finished changing me to " + newValue);
});

Finally, if you'd like to do a little something extra when a function is called, use the following:

gui.add(obj, "functionName").onFire(function() {
   alert("You called a function with dat.gui");
});

Let's say you have a variable that changes by itself from time to time. If you'd like the DAT.GUI to reflect those changes, use the listen() method.

gui.add(obj, "changingProperty").listen();

By default, dat.gui will create an internal interval that checks for changes in the values you've marked with listen(). If you'd like to check for these changes in an interval of your own definition, use the following:

gui.autoListen = false; // disables internal interval
gui.add(obj, "changingProperty").listen();

// Make your own loop
setInterval(function() {
    gui.listen(); // updates values you've marked with listen()
}, 1000 / 60);

Alternatively, you can forego calling listen() on individual controllers, and instead choose to monitor changes in all values controlled by your gui.

gui.autoListen = false; // disables internal interval
gui.add(obj, "add");
gui.add(obj, "lotsa");
gui.add(obj, "properties");

// Make your own loop
setInterval(function() {
    gui.listenAll(); // updates ALL values managed by this gui
}, 1000 / 60);

You can instantiate multiple DAT.GUI objects and name them however you'd like.

var gui1 = new DAT.GUI();
var gui2 = new DAT.GUI();

// The name function overwrites the "Show Controls" text.
gui1.name("Utilities");
gui2.name("Camera Placement");

By default, dat.gui panels will be automatically added to the HTML document and fixed to the top of the screen. You can disable this behavior / styling and append the gui DOM element to a container of your choosing.

// Notice this belongs to the DAT.GUI class (uppercase)
// and not an instance thereof.
DAT.GUI.autoPlace = false;

var gui = new DAT.GUI();

// Do some custom styles ...
gui.domElement.style.position = "absolute";
gui.domElement.style.top = "20px";
gui.domElement.style.left = "20px";

document.getElementById("my-gui-container").appendChild( gui.domElement );

1. dat.gui panels are resizeable. Drag the show/hide button.
2. Press 'H' to show/hide GUI's.