javascript array push works but not assigning to its index

Question

Although this is done in vuejs, I strongly believe this is plain javascript related, I have this doc_types array, when I try to assign some value to its index it isn't working, but when I try to push it works fine..

data: function () {
    return {
      doc_types: [],
    }
  },
  methods:  {
      populateDocType() {

                 this.doc_types.push(response.data); //this works
                 this.doc_types[0] = response.data //this doesn't...no errors though..just the array is unmodified..

      }
  }

Can you log this.doc_types[0] before and after trying to assign data? — Justinas
– Justinas, Commented Sep 3, 2018 at 12:11
the first statement adds to the array a new value, while the second assigns to the first value of the array the result. which leaves the array unmodified, since its size didnt change, but the value of the first element did. this.doc_types = response.data would assign to the array the value (probably an array). — Rafael Herscovici
– Rafael Herscovici, Commented Sep 3, 2018 at 12:16

tony19 · Accepted Answer · 2022-07-15 02:51:16Z

3

I'm assuming when you say it doesn't work that trigger the listeners it should, not that the data structure itself doesn't get changed.

This is a noted caveat in Vue's change detection.

The solution is to use Vue's workaround

Vue.set(array, indexOfItem, newValue)

Or in your case

Vue.set(this.doc_types, 0, response.data)

This is explained more fully here: https://v2.vuejs.org/v2/guide/list.html#Caveats

edited Jul 15, 2022 at 2:51

tony19

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answered Sep 3, 2018 at 12:14

SamCosta1

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