vue watch newValue same oldValue bugs All In One

vue watch newValue same oldValue bugs All In One

JSON.stringify

watch: {
    obj: function(newValue, oldValue) {
      // ❌
      console.log(newValue, oldValue);
      // ✅
      console.log(JSON.stringify(oldValue) === JSON.stringify(newValue));
    },
  }

old value will be the same as new value ❌

Note: when mutating (rather than replacing) an Object or an Array, the old value will be the same as new value because they reference the same Object/Array.
Vue doesn’t keep a copy of the pre-mutate value.

https://vuejs.org/v2/api/#vm-watch

refs

https://stackoverflow.com/questions/62729380/vue-watch-outputs-same-oldvalue-and-newvalue

https://github.com/vuejs/vue/issues/2164#issuecomment-828139247

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