Delting object from array in vue props : I am getting a very strange behaviour while splicing the object from array. 

I have a js array with objects. I am passing it via props and populating a navigation based on it. Now when I try to delete it inside `created hood` it deleted half and keep half. 
Here is the code. Very simple

    props: {
     navItems: {
      type: Array,
     },
    },

 In created hook I have 

    let nav = this.navItems
    for(let j in nav){
      nav.splice(j,1)
    }
    console.log(nav) // print half item from the array. Shouldn't remove all?
    this.nav = nav

Thank you.