Which code is to generate the http-bind request body?

in connection.js, below code is to generate the http-bind URL:
connectionConfig.bosh += ?room=${roomName};

but I could not find which code is used to generate the http-bind request body. like below :

<body rid='4270412592' xmlns='http://jabber.org/protocol/httpbind' sid='3152b599-dd4c-422a-8d7e-16e1177e9965'><iq from='12feeae9-3d97-4ea4-88df-cc8b4f7deadf@meet.pangu.com/25aba785-3461-4462-9e95-bce55513a4a0' to='meet.pangu.com' type='get' xmlns='jabber:client' id='b27129cd-9082-4a7d-822f-1985ae666b00:sendIQ'><query xmlns='http://jabber.org/protocol/disco#info'/></iq><iq to='focus.meet.pangu.com' type='set' xmlns='jabber:client' id='a976650c-f3ab-4673-a607-14673c3af452:sendIQ'><conference xmlns='http://jitsi.org/protocol/focus' room='2222@conference.meet.pangu.com' machine-uid='f541c0320ff3ca2dc1dc86f418149e21'><property name='channelLastN' value='-1'/><property name='disableRtx' value='false'/><property name='enableLipSync' value='true'/><property name='openSctp' value='true'/></conference></iq></body>

does anybody which js code is used to generate http-bind request body from web client ?

This is strophe, the library we use for xmpp connections: https://github.com/strophe/strophejs/