Class SpringJoint

A spring/damper constraint between two anchor points on two bodies.

Applies a spring force that pulls or pushes the anchors toward a target restLength. The spring behavior is controlled by frequency (Hz) and damping (ratio), inherited from Constraint.

Unlike DistanceJoint, a SpringJoint:

Is always soft — there is no rigid/stiff mode.
Has a single restLength instead of a [jointMin, jointMax] range.
Applies force in both directions (compression and extension).
Never goes slack — the spring always exerts a restorative force.

Ideal for: vehicle suspension, soft-body connections, ragdoll hair/cloth, bouncy UI animations, bridge/rope segments, trampolines.

Example

const spring = new SpringJoint(
  body1, body2,
  Vec2.weak(0, 0),   // anchor on body1 (local)
  Vec2.weak(0, 0),   // anchor on body2 (local)
  100,               // rest length (pixels)
);
spring.frequency = 5;  // 5 Hz oscillation
spring.damping = 0.5;  // underdamped (bouncy)
spring.space = space;

Hierarchy (View Summary)

Constraint
- SpringJoint

Index

Constructors

constructor

new SpringJoint(
    body1: Body | null,
    body2: Body | null,
    anchor1: Vec2,
    anchor2: Vec2,
    restLength: number,
): SpringJoint
Parameters
- body1: Body | null
  First body, or null for a static world anchor.
- body2: Body | null
  Second body, or null for a static world anchor.
- anchor1: Vec2
  Anchor point in body1's local space (disposed if weak).
- anchor2: Vec2
  Anchor point in body2's local space (disposed if weak).
- restLength: number
  Equilibrium distance between anchors (must be >= 0).
Returns SpringJoint
Overrides Constraint.constructor
- Defined in packages/nape-js/src/constraint/SpringJoint.ts:77

Properties

debugDraw

debugDraw: boolean = true

Accessors

active

get active(): boolean
Whether the constraint is currently active (enforced by the solver).

Deactivating a constraint suspends it without removing it from the space.

Returns boolean
Default Value
true
Inherited from Constraint.active
- Defined in packages/nape-js/src/constraint/Constraint.ts:149
set active(value: boolean): void
Parameters
- value: boolean
Returns void
Inherited from Constraint.active
- Defined in packages/nape-js/src/constraint/Constraint.ts:152

anchor1

get anchor1(): Vec2
Anchor point on body1 in local coordinates.

Returns Vec2
- Defined in packages/nape-js/src/constraint/SpringJoint.ts:237
set anchor1(value: Vec2): void
Parameters
- value: Vec2
Returns void
- Defined in packages/nape-js/src/constraint/SpringJoint.ts:243

anchor2

get anchor2(): Vec2
Anchor point on body2 in local coordinates.

Returns Vec2
- Defined in packages/nape-js/src/constraint/SpringJoint.ts:258
set anchor2(value: Vec2): void
Parameters
- value: Vec2
Returns void
- Defined in packages/nape-js/src/constraint/SpringJoint.ts:264

body1

get body1(): Body
First body. null treats the anchor as a static world point.

Returns Body
- Defined in packages/nape-js/src/constraint/SpringJoint.ts:163
set body1(value: Body | null): void
Parameters
- value: Body | null
Returns void
- Defined in packages/nape-js/src/constraint/SpringJoint.ts:167

body2

get body2(): Body
Second body. null treats the anchor as a static world point.

Returns Body
- Defined in packages/nape-js/src/constraint/SpringJoint.ts:198
set body2(value: Body | null): void
Parameters
- value: Body | null
Returns void
- Defined in packages/nape-js/src/constraint/SpringJoint.ts:202

breakUnderError

get breakUnderError(): boolean
When true, the constraint breaks if the positional error exceeds maxError.

Returns boolean
Default Value
false
Inherited from Constraint.breakUnderError
- Defined in packages/nape-js/src/constraint/Constraint.ts:325
set breakUnderError(value: boolean): void
Parameters
- value: boolean
Returns void
Inherited from Constraint.breakUnderError
- Defined in packages/nape-js/src/constraint/Constraint.ts:328

breakUnderForce

get breakUnderForce(): boolean
When true, the constraint breaks (fires a BREAK event) if the applied force exceeds maxForce in a single step.

Returns boolean
Default Value
false
Inherited from Constraint.breakUnderForce
- Defined in packages/nape-js/src/constraint/Constraint.ts:311
set breakUnderForce(value: boolean): void
Parameters
- value: boolean
Returns void
Inherited from Constraint.breakUnderForce
- Defined in packages/nape-js/src/constraint/Constraint.ts:314

cbTypes

get cbTypes(): object
The set of CbTypes assigned to this constraint. Used to filter which listeners respond to this constraint's events.

Returns object
Inherited from Constraint.cbTypes
- Defined in packages/nape-js/src/constraint/Constraint.ts:376

compound

get compound(): Compound | null
The compound this constraint belongs to, or null. When set, the constraint's space is managed by the compound.

Returns Compound | null
Inherited from Constraint.compound
- Defined in packages/nape-js/src/constraint/Constraint.ts:121
set compound(value: Compound | null): void
Parameters
- value: Compound | null
Returns void
Inherited from Constraint.compound
- Defined in packages/nape-js/src/constraint/Constraint.ts:125

damping

get damping(): number
Damping ratio for soft constraints (stiff = false).

0 = undamped (oscillates freely), 1 = critically damped. Values > 1 are overdamped. Must be >= 0. Ignored when stiff is true.

Returns number
Default Value
1
Inherited from Constraint.damping
- Defined in packages/nape-js/src/constraint/Constraint.ts:241
set damping(value: number): void
Parameters
- value: number
Returns void
Inherited from Constraint.damping
- Defined in packages/nape-js/src/constraint/Constraint.ts:244

frequency

get frequency(): number
Spring frequency in Hz for soft constraints (stiff = false).

Higher values make the spring stiffer; lower values make it bouncier. Must be > 0. Ignored when stiff is true.

Returns number
Default Value
10
Inherited from Constraint.frequency
- Defined in packages/nape-js/src/constraint/Constraint.ts:216
set frequency(value: number): void
Parameters
- value: number
Returns void
Inherited from Constraint.frequency
- Defined in packages/nape-js/src/constraint/Constraint.ts:219

ignore

get ignore(): boolean
When true the constraint is completely ignored by the engine — bodies are not woken, no impulse is applied, and no callbacks fire.

Returns boolean
Default Value
false
Inherited from Constraint.ignore
- Defined in packages/nape-js/src/constraint/Constraint.ts:183
set ignore(value: boolean): void
Parameters
- value: boolean
Returns void
Inherited from Constraint.ignore
- Defined in packages/nape-js/src/constraint/Constraint.ts:186

isSleeping

get isSleeping(): boolean
Whether the constraint's simulation component is currently sleeping.

Only valid when the constraint is active and in a space — throws otherwise.

Returns boolean
Inherited from Constraint.isSleeping
- Defined in packages/nape-js/src/constraint/Constraint.ts:352

maxError

get maxError(): number
Maximum positional error (in pixels) allowed before breaking.

Only meaningful when breakUnderError is true. Must be >= 0. Infinity disables the limit.

Returns number
Default Value
Infinity
Inherited from Constraint.maxError
- Defined in packages/nape-js/src/constraint/Constraint.ts:290
set maxError(value: number): void
Parameters
- value: number
Returns void
Inherited from Constraint.maxError
- Defined in packages/nape-js/src/constraint/Constraint.ts:293

maxForce

get maxForce(): number
Maximum force (in Newtons) the constraint may apply per step.

When the required force exceeds this value the constraint becomes slack. If breakUnderForce is true the constraint breaks instead. Must be >= 0. Infinity disables the limit.

Returns number
Default Value
Infinity
Inherited from Constraint.maxForce
- Defined in packages/nape-js/src/constraint/Constraint.ts:267
set maxForce(value: number): void
Parameters
- value: number
Returns void
Inherited from Constraint.maxForce
- Defined in packages/nape-js/src/constraint/Constraint.ts:270

removeOnBreak

get removeOnBreak(): boolean
When true (default), the constraint is automatically removed from its space when it breaks. Set to false to keep it in the space after breaking.

Returns boolean
Default Value
true
Inherited from Constraint.removeOnBreak
- Defined in packages/nape-js/src/constraint/Constraint.ts:340
set removeOnBreak(value: boolean): void
Parameters
- value: boolean
Returns void
Inherited from Constraint.removeOnBreak
- Defined in packages/nape-js/src/constraint/Constraint.ts:343

restLength

get restLength(): number
Equilibrium distance between anchors (pixels, must be >= 0).

Returns number
- Defined in packages/nape-js/src/constraint/SpringJoint.ts:283
set restLength(value: number): void
Parameters
- value: number
Returns void
- Defined in packages/nape-js/src/constraint/SpringJoint.ts:286

space

get space(): Space | null
The space this constraint belongs to, or null if not in a space.

Assign to add/remove the constraint from a space:
```
joint.space = mySpace;  // adds to space
joint.space = null;     // removes from space
```
Cannot be set if the constraint belongs to a Compound.
Returns Space | null
Inherited from Constraint.space
- Defined in packages/nape-js/src/constraint/Constraint.ts:82
set space(value: Space | null): void
Parameters
- value: Space | null
Returns void
Inherited from Constraint.space
- Defined in packages/nape-js/src/constraint/Constraint.ts:86

stiff

get stiff(): boolean
SpringJoint is always soft — setting stiff to true is not allowed. Use DistanceJoint if you need a rigid distance constraint.

Returns boolean
Overrides Constraint.stiff
- Defined in packages/nape-js/src/constraint/SpringJoint.ts:304
set stiff(_value: boolean): void
When true (default) the constraint is stiff/rigid. When false the constraint uses a soft spring model driven by frequency and damping.
Parameters
- _value: boolean
Returns void
Default Value
true
Overrides Constraint.stiff
- Defined in packages/nape-js/src/constraint/SpringJoint.ts:307

userData

get userData(): Record<string, unknown>
Arbitrary user data attached to this constraint. Lazily initialized to {} on first access.

Returns Record<string, unknown>
Inherited from Constraint.userData
- Defined in packages/nape-js/src/constraint/Constraint.ts:365

Methods

bodyImpulse

bodyImpulse(body: Body): Vec3
The impulse applied to body by this constraint in the last simulation step, expressed as a Vec3 (fx, fy, torque).
Parameters
- body: Body
Returns Vec3
Overrides Constraint.bodyImpulse
- Defined in packages/nape-js/src/constraint/SpringJoint.ts:325

copy

copy(): Constraint
Creates and returns a copy of this constraint with the same parameters. The copy is not automatically added to a space.

Returns Constraint
Inherited from Constraint.copy
- Defined in packages/nape-js/src/constraint/Constraint.ts:419

impulse

impulse(): MatMN
The impulse applied by this constraint in the last simulation step.

The shape of the returned MatMN depends on the constraint's degrees of freedom (e.g., 1×1 for AngleJoint/MotorJoint, 2×1 for PivotJoint/LineJoint, 3×1 for WeldJoint).

Returns MatMN
Overrides Constraint.impulse
- Defined in packages/nape-js/src/constraint/SpringJoint.ts:315

toString

toString(): string
Returns string
Inherited from Constraint.toString
- Defined in packages/nape-js/src/constraint/Constraint.ts:423

visitBodies

visitBodies(lambda: (body: Body) => void): void
Invokes fn once for each distinct body linked to this constraint.
Parameters
- lambda: (body: Body) => void
Returns void
Overrides Constraint.visitBodies
- Defined in packages/nape-js/src/constraint/SpringJoint.ts:342

Class SpringJoint

Example

Hierarchy (View Summary)

Index

Constructors

Properties

Accessors

Methods

Constructors

constructor

Parameters

Returns SpringJoint

Properties

debugDraw

Accessors

active

Returns boolean

Default Value

Parameters

Returns void

anchor1

Returns Vec2

Parameters

Returns void

anchor2

Returns Vec2

Parameters

Returns void

body1

Returns Body

Parameters

Returns void

body2

Returns Body

Parameters

Returns void

breakUnderError

Returns boolean

Default Value

Parameters

Returns void

breakUnderForce

Returns boolean

Default Value

Parameters

Returns void

cbTypes

Returns object

compound

Returns Compound | null

Parameters

Returns void

damping

Returns number

Default Value

Parameters

Returns void

frequency

Returns number

Default Value

Parameters

Returns void

ignore

Returns boolean

Default Value

Parameters

Returns void

isSleeping

Returns boolean

maxError

Returns number

Default Value

Parameters

Returns void

maxForce

Returns number

Default Value

Parameters

Returns void

removeOnBreak