Regarding how to place BitMEX Post-Only Limit Orders and Batch Orders using IO (an example)

Use the IO function and refer to the BitMEX documentation for specific parameters: https://www.fmz.com/bbs-topic/3666

Market-making order (passive execution only)

var id = exchange.IO("api", "POST", "/api/v1/order", "symbol=XBTUSD&side=Buy&orderQty=1&price=5000&execInst=ParticipateDoNotInitiate")

Batch order placement

var bulk = []
bulk.push({symbol:'XBTUSD', side:'Buy', orderQty:100, price:5000, execInst:'ParticipateDoNotInitiate'})
bulk.push({symbol:'XBTUSD', side:'Buy', orderQty:200, price:5100, execInst:'ParticipateDoNotInitiate'})
var param = "orders=" + JSON.stringify(bulk)
var ids = exchange.IO("api", "POST", "/api/v1/order/bulk", param)
Log(ids)

Cancel all orders

exchange.IO("api","DELETE","/api/v1/order/all","symbol=XBTUSD")