const unit = 'k37Xlns198EHCtubX5X0kqbrnC9XYVTa0aFpR78gidM=';client.api.getJoint(unit, function(err, result) {console.log(result);});
Try on JSFiddle.
{joint: {unit: {unit: 'k37Xlns198EHCtubX5X0kqbrnC9XYVTa0aFpR78gidM=',version: '1.0',alt: '1',witness_list_unit: 'oj8yEksX9Ubq7lLc+p6F2uyHUuynugeVq4+ikT67X6E=',last_ball_unit: '9tIFlniHyoVJEp0i+WHMTZqnnR1UqgAhrIWFRkgE8m0=',last_ball: 'qxl8Rq1IjVUICgbm9A1+d+ZC3pG75HoDEFTchdL6scg=',headers_commission: 344,payload_commission: 123,main_chain_index: 2870558,timestamp: 1529756195,parent_units: ['0V3X7wyTl/17YX83YbjFgyJ2LRNxbgT5jXQOdLvZR2A=','HJoe07dHWj5fH5s7PMgwbtryM/o14YERshGVz4cP1BQ='],authors: [{address: 'S7N5FE42F6ONPNDQLCF64E2MGFYKQR2I',authentifiers: {r: 'nNx6QBfwIQkZydLEDXs/di0U5wqFaw4L15OCGICFGkwDgDh3KK+ks5hxFoUhSLxiZZIeNt1gIjmpKFv+bIiDtQ=='}}],messages: [{app: 'payment',payload_hash: 'g0eNA+42F6Zxx650BLNxUKAwx3R3HJ/pC1tjxXVg8Lg=',payload_location: 'inline',payload: {inputs: [{type: 'witnessing',from_main_chain_index: 580671,to_main_chain_index: 580684}],outputs: [{address: 'S7N5FE42F6ONPNDQLCF64E2MGFYKQR2I',amount: 79}]}}]},ball: 'XRz6FcvpNLjrzXkCeQGIM/ekqQTrmB/kBEpn1grsrI0='}}
"12. Unit structure" (page 15) https://obyte.org/Byteball.pdf