使用地图迭代对象数组，直到倒数第二个对象

Question

I am having an array of objects where all objects have the same keys except the last object. Think like array have values and to denote all these values as a whole I have a key I am pushing the key at last along with the values in the array.

homeTask is a list of object which is the values and homeTaskKey is the key to represent the homeTask

        res.data.resultSet.homeTask.forEach(element => {
                      var singleEvent={
                        task:'',
                        taskDuration:'',
                        status:'',
                      };

                      singleEvent.task=element.task;
                      singleEvent.taskDuration=element.taskDuration;
                      singleEvent.status=element.status;

                      newEvents.push(singleEvent);


                    });
                    newEvents.push(res.data.resultSet.homeTaskKey);


                   addEvent(newEvents);
              }

addEvent is props method of parent component where I am setting the array to state variable name as events which is array type.

When I iterate over events using map I want to skip the last object since it does not have keys like task, taskDuration and status. Therefore it won't give any problem when I fetch those values.

Answer 1

You could still use map , but simply pop the last element off once the map completes. For example:

const newEvents = homeTask.map(({ task, taskDuration, status }) => ({
  task, taskDuration, status
}))
newEvents.pop()
addEvent(newEvents)

Or just replace the last item with your taskkey, as you know the last item will be junk:

newEvents[newEvents.length - 1] = res.data.resultSet.homeTaskKey

Or just slice the array prior to mapping, and then push the taskKey at the end like you were doing. slice is safe to perform on your prop, as it shallow copies.

---

Or most importantly, ask yourself why you have this entirely weird data structure that has the key appended on the end. Perhaps rethink your data and not create this problem for yourself in the first place.

Answer 2

events.slice(0, events.length-1).map(<function>);

this will ignore the last element and all n-1 entries will be fed to map

UPDATE :

the array name is events not event therefore it should be events.length

Answer 3

res.data.resultSet.homeTask.forEach((element,index) => {})

函数的第二个参数是索引，可以通过将其与数组的总长度进行比较来使用它来标识倒数第二个元素。

Answer 4

hmm you can try with this

res.data.resultSet.homeTask.forEach(element => {
    if(!element.task)
        return false;
    ...bla bla bla
}

Answer 5

The map() method creates a new array with the results of calling a function for every array element.

So it creates an array of same length from source array.

What you need is filter() https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter

Something like this;

const tasks = res.data.resultSet.homeTask.filter((element) => {
  const { task, taskDuration, status } = element;
  return task && taskDuration && status; 
});