node_modules/@plotly/mapbox-gl/src/style/zoom_history.js

// @flow

class ZoomHistory {
    lastZoom: number;
    lastFloorZoom: number;
    lastIntegerZoom: number;
    lastIntegerZoomTime: number;
    first: boolean;

    constructor() {
        this.first = true;
    }

    update(z: number, now: number) {
        const floorZ = Math.floor(z);

        if (this.first) {
            this.first = false;
            this.lastIntegerZoom = floorZ;
            this.lastIntegerZoomTime = 0;
            this.lastZoom = z;
            this.lastFloorZoom = floorZ;
            return true;
        }

        if (this.lastFloorZoom > floorZ) {
            this.lastIntegerZoom = floorZ + 1;
            this.lastIntegerZoomTime = now;
        } else if (this.lastFloorZoom < floorZ) {
            this.lastIntegerZoom = floorZ;
            this.lastIntegerZoomTime = now;
        }

        if (z !== this.lastZoom) {
            this.lastZoom = z;
            this.lastFloorZoom = floorZ;
            return true;
        }

        return false;
    }
}

export default ZoomHistory;