THREE.KeyframeTrack: track type undefined, can not parse

Error message

THREE.KeyframeTrack: track type undefined, can not parse

What it means

Thrown by parseKeyframeTrack() when a track object in an AnimationClip JSON has no 'type' field at all. The type is required to select the KeyframeTrack subclass via getTrackTypeForValueTypeName(); without it, parsing cannot proceed. This fires before the unsupported-type-name check (error [14]).

Source

Thrown at src/animation/AnimationClip.js:458

		case 'boolean':

			return BooleanKeyframeTrack;

		case 'string':

			return StringKeyframeTrack;

	}

	throw new Error( 'THREE.KeyframeTrack: Unsupported typeName: ' + typeName );

}

function parseKeyframeTrack( json ) {

	if ( json.type === undefined ) {

		throw new Error( 'THREE.KeyframeTrack: track type undefined, can not parse' );

	}

	const trackType = getTrackTypeForValueTypeName( json.type );

	if ( json.times === undefined ) {

		const times = [], values = [];

		AnimationUtils.flattenJSON( json.keys, times, values, 'value' );

		json.times = times;
		json.values = values;

	}

	// derived classes can define a static parse method
	if ( trackType.parse !== undefined ) {

View on GitHub (pinned to da05705fa3)

Solutions

Inspect each track in the clip JSON and add the missing 'type' field with a supported value-type name (e.g. 'vector3', 'quaternion', 'scalar').
Re-export the clip from the source (Blender/glTF) rather than hand-editing, so type is always populated.
If loading untrusted animation data, validate up front that every track has a non-empty type before calling AnimationClip.parse().

Example fix

// before
{ "tracks": [ { "name": "x.position", "times": [0], "values": [0] } ] }
// -> 'track type undefined, can not parse'

// after — add the type field
{ "tracks": [ { "name": "x.position", "type": "vector3", "times": [0], "values": [0,0,0] } ] }

Defensive patterns

Strategy: validation

Validate before calling

function validateClipTracks( clipJson ) {
  for ( const t of clipJson.tracks || [] ) {
    if ( t.type === undefined ) throw new Error( `track '${t.name}' is missing 'type'` );
  }
}

Type guard

function trackHasType( track ) {
  return track !== null && typeof track === 'object' && typeof track.type === 'string' && track.type.length > 0;
}

Try / catch

try {
  clip = AnimationClip.parse( json );
} catch ( err ) {
  if ( /track type undefined/.test( err.message ) ) {
    console.error( 'Skipping clip with untyped track(s).', json );
    clip = null;
  } else throw err;
}

Prevention

Always serialize tracks with a 'type' field; re-export rather than hand-edit clip JSON.
Before AnimationClip.parse, assert every track has a non-empty type.
Audit custom exporters to ensure type is emitted for every track.

When it happens

Trigger: An animation clip JSON whose tracks array contains an entry missing the type key. Manually constructing clip JSON and omitting type. A truncated/malformed serialization where the type field was dropped.

Common situations: Hand-editing exported animation JSON. A bug in a custom exporter that skips the type field for certain tracks. Loading a partially-corrupt clip file.

Related errors

AI-assisted analysis of mrdoob/three.js@da05705fa3 (2026-08-12). Data as JSON: /api/errors/bbb05c87f23340a9. Report an issue: GitHub.