從過濾可觀察數組中獲取第一個值

Question

假設我有一個 observable 數組，其結構如下：

let arr = Observable.of([{a: null}, {a: [1,2,3,4]}, {a: [1,2,3]}, {a: null}])

我想取出a不為null的第一個對象。 我怎樣才能返回{a: [1,2,3,4]} ？

Answer 1

你可以試試這樣的

let arr = Observable.of([{a: null}, {a: [1,2,3,4]}, {a: [1,2,3]}, {a: null}])

arr
.pipe(
  // with this map you transform the array emitted by the source into the first item where a is not null
  map(a => a.find(item => !!item.a))  // find is the array method
)
.subscribe(
  // the data emitted here can be null if all items in the original array have an a property null
  data => console.log("I am the first item with a not null, if any", data)
)