watch array in vue.js v2

script.js

// https://ahmedelwerdany.github.io/posts/watch-many-in-vue-js/
function watchMany (arrayOfKeys, value) {
    const object = {}
    for (let i = 0; i < arrayOfKeys.length; i++) {
        object[arrayOfKeys[i]] = value
    }

    return object
}

export default {
 name: 'Form',
 data: () => ({
  shose_price: 0,
  hat_price: 0,
  short_price: 0,
 }),
 watch: {
     ...watchMany(['shose_price', 'hat_price','short_price'], function (value) {
         if (typeof value !== 'number') {
             return
         }
         this.total = this.shoes_price + this.short_price + this.hat_price
     }),
     total : function () {
         this.total_with_disscount = this.total - (this.total * this.discount)
     }
 }
}