How to reference data variable from another data variable in Vue 2? [duplicate]

You need to do something like this to make it work:

#1st way

data() {
    let defaultNames = [];
    return {
      names: defaultNames,
      length: defaultNames.length
    }
}

#2nd way — using computed data (the better way):

data() {
    return {
      names: [],
    }
},
computed: {
    length() {
        return this.names.length;
    }
}