feast/src/main.ts

import Vue from 'vue'
import App from '@/App.vue'

declare global {
  interface Array<T> {
    joinGeneral (item: T, endItem: T|null): Array<T>;
    /* eslint-disable-next-line */
    unique (predicate?: (elem: T) => any): Array<T>;
  }
}

/* eslint-disable-next-line */
Array.prototype.joinGeneral = function (item, endItem = null) {
  if (endItem === null) {
    return this.slice(0, -1).flatMap(x => [x, item]).concat(this.slice(-1))
  } else {
    return this.slice(0, -2).flatMap(x => [x, item]).concat(this.slice(-2, -1).flatMap(x => [x, endItem])).concat(this.slice(-1))
  }
}

/* eslint-disable-next-line */
Array.prototype.unique = function<T> (predicate?: (elem: T) => any): Array<T> {
  const set = new Set()
  const result: Array<T> = [] as T[]
  this.forEach(elem => {
    // if there is no predicate, just use the identity function
    const predResult = (predicate ?? (x => x))(elem)
    if (!set.has(predResult)) {
      set.add(predResult)
      result.push(elem)
    }
  })
  return result
}

Vue.config.productionTip = false

new Vue({
  render: h => h(App)
}).$mount('#app')