array issue

 1.today i need to push array to an object calss i tried but got an error.

so i declared the array where exactly i need 
when check box checked(gatein(dms)) then i declared the array with name damage codes then the issue resolved.

2.2nd issue every time checkbox selected then the array become null so i given length condition then

its working fine 

finaly this is how to give array to the class.

selectDamagedata(e){debugger

    if( this.tripInformations.damagecodes.length==0){

      this.tripInformations.damagecodes=[]

    }

    this.tripInformations.damagecodes.push(e)

}