js array_column

var aa = {"id":93,"method":"call.setAdviseMedia","params":{"nid":"91202001636","medias":[{"operator":5,"layoutEnable":true,"streams":[{"modeIndex":8,"key":"layout_1","type":"main","attachment":{"rect":[0,0.083,0,0.5,0.5],"nid":"2336136791"},"layoutType":0},{"modeIndex":8,"key":"layout_2","type":"main","attachment":{"rect":[0.5,0.083,0,0.5,0.5],"nid":"1141099640"},"layoutType":0},{"modeIndex":8,"key":"layout_3","type":"main","attachment":{"rect":[0,0.583,0,0.333,0.333],"nid":"3371156156"},"layoutType":0},{"modeIndex":8,"key":"layout_4","type":"main","attachment":{"rect":[0.333,0.583,0,0.333,0.333],"nid":"8342474883"},"layoutType":0},{"modeIndex":8,"key":"layout_5","type":"main","attachment":{"rect":[0.666,0.583,0,0.333,0.333],"nid":""},"layoutType":0}]}]}}


var bb =a.params.medias.map( item => {
    return item.streams.map( data => {
	return data.attachment
})
})