[Vuejs]-How to initialize data in component according to the received props and don't lose reactivity

There are multiple problems

1. In your examples you don’t show how you initialize your data() but assuming from the code this.markedSteps = []; in initializeMarkedSteps I think you have no markedSteps in data(). That’s problem number 1. Properties in data are only reactive if they existed when the instance was created (add markedSteps: [] into data())

2. Due to limitations in JavaScript, Vue cannot detect changes to an array when you directly set an item with the index – use Vue.set(this.markedSteps, i, true) instead