Class to do a batch set using firestore admin object.

firebase-batch.js

/**
 * Class to handle batch set to docs maximum 500 per commit
 */
class BatchSetHandler {
	/**
	 * Construct BatchSetHandler object
	 * @param {firebase.firestore.WriteBatch} dbBatch
	 * @param {function} commitCallback Callback after commit promise is resolved.
	 */
	constructor( dbBatch, commitCallback ) {

		if ( typeof commitCallback !== 'function' ) {
			commitCallback = ( count ) => {
				console.log( 'Committed ' + count + ' transactions.' );
			};
		}
		this.batch = dbBatch;
		this.count = 0;
		this._promises = [];
		this.commitCallback = commitCallback;
	}

	/**
	 * Set object to docRef
	 * Handles maximum 500 items in one batch
	 * @param {firebase.firestore.DocumentReference} docRef Document reference
	 * @param {object} obj Object to push to Document reference
	 */
	set( docRef, obj ) {
		batchSetHandle.batch.set( docRef, obj, {merge: true} );
		this.count++;
		if ( batchSetHandle.count > 499 ) {
			this.commit();
		}
	}

	/**
	 * Commit the batch
	 */
	commit() {
		const that = this;
		this._promises.push(
			this.batch.commit().then( () => {
				const count = that.count;
				that.count = 0;
				return this.commitCallback( count, that ) || null;
			} )
		);
	}

	/**
	 * Get all promises from commits
	 * @returns {Array} Promise[]
	 */
	promises() {
		return this._promises;
	}
}