Temporarily Disable Ammo.js Constraints

This article explains how to temporarily disable a specific physics constraint in ammo.js—the JavaScript port of the Bullet physics engine—without destroying the constraint object. You will learn the two primary methods for accomplishing this: removing the constraint from the simulation world and using the built-in enablement toggle.

Method 1: Removing and Re-adding the Constraint (Recommended)

The most reliable and performance-friendly way to temporarily disable a constraint in ammo.js is to remove it from the dynamics world simulation. This keeps the constraint object and all its configuration settings intact in memory, allowing you to re-enable it later without recreating it.

To Disable:

To stop the constraint from affecting your physics bodies, remove it from your dynamics world instance:

physicsWorld.removeConstraint(constraint);

To Re-enable:

When you are ready to activate the constraint again, simply add it back to the physics world:

physicsWorld.addConstraint(constraint, disableCollisionsBetweenLinkedBodies);

(Note: disableCollisionsBetweenLinkedBodies is an optional boolean that determines whether the two connected bodies should collide with each other while joined).

By using this method, you avoid the overhead of destroying and rebuilding complex constraints (like hinges or sliders), and you prevent memory leaks by avoiding unnecessary garbage collection of WebAssembly objects.

Method 2: Using the setEnabled Method

The Bullet physics engine includes a built-in toggle for constraint activation. Depending on the specific build and WebIDL binder settings of your ammo.js library, you can toggle the constraint directly using the setEnabled function.

To Disable:

constraint.setEnabled(false);

To Re-enable:

constraint.setEnabled(true);

Important Compatibility Note

Because ammo.js is a wrapper compiled from C++, not all builds expose the setEnabled method to JavaScript. If your build of ammo.js throws an “is not a function” error when calling setEnabled, you must use Method 1 instead, which is universally supported across all versions of the library.