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Build Status Known Vulnerabilities Language grade: JavaScript Total alerts

Provides EventEmitter framework for market/auction implementations, order storage and insertion/cancellation/expiration functionality

Breaking Changes for v3

Module changes

v3 is ESM whereas versions 2 and earlier were commonjs.

removing babel dependencies

v3 is not compiled with Babel

minor change to this.reduceQ()

will now throw clearer error if parameters are mismatched

Programmers documentation

jsdoc pages for market-engine


npm install market-engine --save


import MarketEngine from 'market-engine'; // ES Module


MarketEngine is used as a base class for building classes representing market exchanges with some set of customized rules.

MarketEngine does the housekeeping of maintaining an active list of orders, a trash list, and provides a framework for handline new orders and trades, without specifying the ultimate form of orders or the rules of trade.


For a subclass implementing sequential double auction trading rules, see market-example-contingent


MarketEngine is an EventEmitter. Here is an event reference.

bump -- Fired when one or more orders are cancelled or expired.

clear -- Fired when the market has been reset to an "empty" state with no orders.

before-order -- Fired before each order is processed by the market. Allows for rejection of orders.

order -- Fired when an order is ready for processing, i.e. if not rejected in before-order

trade -- Fired when a trade between orders is ready for processing.

trade-cleanup -- Fired to clean up after trade has been processed.

after-trade -- Fired after trade-cleanup

Setting Event Handlers

In the explanations below, XMarket is a variable containing an instance of MarketEngine.

XMarket.on('clear', function(){...})

specifies function to call when the market data is cleared

XMarket.on('before-order', function(neworder, reject){ ... })

specifies function to call before each order.

If neworder is an Array, a timestamp from will be in neworder[0]

If neworder is an Object, the timestamp is in neworder.ts

Any event handler for before-order may reject an order, by using the reject function that is supplied as a 2nd parameter, like this: return reject(neworder)

XMarket.on('order', function(neworder){ ... })

specifies function to call after each order. Array orders will have the ordernum and timestamp prepended. Object orders will have the ordernum in neworder.num and the timestamp in neworder.ts

XMarket.on('trade', function(tradespec){ ... })

specifies function to call after each trade

XMarket.on('trade-cleanup', function(tradespec){ ... })

specifies function to call to clean up after each trade. The first handler attached by default reduces the quantity field of each order in the tradespec and marks the order as trash if the quantity reaches zero.

XMarket.on('after-trade', function(tradespec){ ... })

specifies function to call after the trade event handlers and the trade-cleanup handlers have completed.

##Functions, also see JSdoc documentation.


cancels and/or expires any orders in the active list this.a depending on the timestamp and id in neworder and the setting of the cancelReplace column in neworder. The active list is always scanned for expiring orders, but will only be scanned for cancellation if the cancelReplace column is truthy in neworder.


clears the active list this.a=[], the trash list this.trash=[] and resets this.count to 0, then emits "clear"

Emits: clear()


processes neworder, as follows:

  1. fires before-order
  2. exits if order rejected by a before-order handler
  3. prepends/sets order number and timestamp as first two fields of neworder array
  4. calls MarketEngine.prototype.bump(neworder), trashing any previously expired or cancelled orders
  5. fires order

Code listening for order may call to indicate a trade in accordance with some set of market rules, to be defined by the developer.

Emits: before-order(neworder), order(neworder)
  1. Copies this.o.goods and to tradespec.goods and, if the former are defined.
  2. Fires trade, trade-cleanup and after-trade.

Emits: trade, trade-cleanup, after-trade


Trashes all previous orders by id from the active list this.a .

Trashing an order sets it quantity to 0 and places it in the trash list for deletion by .emptyTrash()

Called by MarketEngine.prototype.bump(neworder) if cancelReplace is indicated.

requires: options.idCol, options.qCol

optional: options.cancelCol (shortens search if a previous cancel/replace found)


Trashes all orders expiring before timestamp ts from the active list this.a.

Trashing an order sets it quantity to 0 and places it in the trash list for deletion by .emptyTrash()

Called by MarketEngine.prototype.bump(neworder) on each neworder

requires: options.txCol, options.qCol

MarketEngine.prototype.reduceQ(ais, qs)

Reduces order quantity of orders locates at indexes in the array ais by the amounts in array qs

requires: options.qCol


Delete any previously trashed orders from active list this.a

Copyright 2016- Paul Brewer, Economic and Financial Technology Consulting LLC




event-driven javascript market engine for economic research, simulations, and experiments







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