解决的任务 function multiply ( a , b ) { return a * b } function tailSwap ( arr ) { let arr0 = arr [ 0 ] . split ( ':' ) ; let arr1 = arr [ 1 ] . split ( ':' ) ; return [ arr0 [ 0 ] + ':' + arr1 [ 1 ] , arr1 [ 0 ] + ':' + arr0 [ 1 ] ] } function countPositivesSumNegatives ( arr ) { if ( ! arr || arr .