Write Array data built in forEach loop back to original Object

Question

I'm using forEach in a vuejs watcher to modify my array of objects. Goal is to have the new value (end_time) in each object at the end. allChapters already contains everything I want but I can't seem to get it written back to the original object.

watch: {
  episode (episode) {
    episode.chapters = episode.chapters.forEach((chapter, index, allChapters) => {
      let endTime = ''
      if (allChapters[(index + 1)]) {
        endTime = allChapters[(index + 1)].start_time
      } else {
        endTime = '99:99:99'
      }
      console.log(index + ': ' + chapter.start_time + ' / ' + endTime)
      allChapters[index] = {
        'start_time': chapter.start_time,
        'title': chapter.title,
        'end_time': endTime
      }
    })
  }
},

you should accept the answer if it solved your problem.

i--
– i--

2018-05-10 15:51:48 +00:00
Commented May 10, 2018 at 15:51 — i--
– i--, Commented May 10, 2018 at 15:51

Gabriele Petrioli · Accepted Answer · 2018-05-10 14:41:12Z

1

the forEach does not return anything, so you end up assigning undefined to the episode.chapters.

Either remove the episode.chapters =

episode (episode) {
    episode.chapters.forEach((chapter, index, allChapters) => { ... })

or use map which returns a new array

watch: {
  episode (episode) {
    episode.chapters = episode.chapters.map((chapter, index, allChapters) => {
      let endTime = ''
      if (allChapters[(index + 1)]) {
        endTime = allChapters[(index + 1)].start_time
      } else {
        endTime = '99:99:99'
      }
      console.log(index + ': ' + chapter.start_time + ' / ' + endTime)

      return {...chapter, 'end_time': endTime};
    })
  }
},

answered May 10, 2018 at 14:41

Gabriele Petrioli

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1 Comment

Helmi Over a year ago

looks like I didn't see the obvious one. Thanks for helping out.

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