BabylonJS/Babylon.js · error · Error

Sounds length does not equal weights length

Error message

Sounds length does not equal weights length

What it means

WeightedSound picks randomly among a set of Sounds using per-sound weights. Its constructor requires the sounds and weights arrays to be the same length so each Sound gets exactly one weight; otherwise it throws this error immediately.

Source

Thrown at packages/dev/core/src/Audio/weightedsound.ts:30

    private _volume: number = 1;
    /** A Sound is currently playing. */
    public isPlaying: boolean = false;
    /** A Sound is currently paused. */
    public isPaused: boolean = false;

    private _sounds: Sound[] = [];
    private _weights: number[] = [];
    private _currentIndex?: number;

    /**
     * Creates a new WeightedSound from the list of sounds given.
     * @param loop When true a Sound will be selected and played when the current playing Sound completes.
     * @param sounds Array of Sounds that will be selected from.
     * @param weights Array of number values for selection weights; length must equal sounds, values will be normalized to 1
     */
    constructor(loop: boolean, sounds: Sound[], weights: number[]) {
        if (sounds.length !== weights.length) {
            throw new Error("Sounds length does not equal weights length");
        }

        this.loop = loop;
        this._weights = weights;
        // Normalize the weights
        let weightSum = 0;
        for (const weight of weights) {
            weightSum += weight;
        }
        const invWeightSum = weightSum > 0 ? 1 / weightSum : 0;
        for (let i = 0; i < this._weights.length; i++) {
            this._weights[i] *= invWeightSum;
        }
        this._sounds = sounds;
        for (const sound of this._sounds) {
            sound.onEndedObservable.add(() => {
                this._onended();
            });

View on GitHub (pinned to 0592b347b8)

Solutions

1. Ensure weights.length === sounds.length before constructing
2. Generate weights programmatically: sounds.map(() => 1)
3. Add a missing weight for every newly added Sound
4. Validate config-derived arrays at load time

Example fix

// before
new WeightedSound(false, sounds, [1, 1]); // sounds has 3 items
// after
const weights = sounds.map(() => 1); // always matches
new WeightedSound(false, sounds, weights);

if (sounds.length !== weights.length) {
    throw new Error(`sounds (${sounds.length}) and weights (${weights.length}) must match`);
}
const ws = new WeightedSound(loop, sounds, weights);

try {
    const ws = new WeightedSound(loop, sounds, weights);
} catch (e) {
    if (e.message.includes("weights length")) {
        const ws = new WeightedSound(loop, sounds, sounds.map(() => 1));
    }
}

When it happens

Trigger: new WeightedSound(loop, sounds, weights) where sounds.length !== weights.length, e.g. 3 sounds with 2 weights or an empty weights array.

Common situations: Building weights dynamically (e.g. from config) that drifts out of sync with the sounds array; forgetting to add a weight when appending a sound; loading sound lists from JSON where some entries are skipped.

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AI-assisted analysis of BabylonJS/Babylon.js@0592b347b8 (2026-08-30). Data as JSON: /api/errors/feb7fce28d265057. Report an issue: GitHub.