prototype expansion

Array.prototype.js

Object.defineProperty(Array.prototype, 'first', {
  get () {
    return this[0]
  },
  
  set (val) {
    if (!this.length) {
      this.push(val)
      return val
    }
    
    this[0] = val 
    return val
  }
})

Object.defineProperty(Array.prototype, 'last', {
  get () {
    if (!this.length) {
      return undefined
    }
    
    return this[this.length - 1]
  },
  
  set (val) {
    if (!this.length) {
      this.push(val)
      return val
    }
    
    this[this.length - 1] = val
    return val
  }
})

Object.defineProperty(Array.prototype, 'max', {
  get () {
    if (!this.length) {
      return undefined
    }
    
    return Math.max(...this)
  },
  
  set (val) {
    if (!this.length) {
      this.push(val)
      return val
    }
    
    const max = Math.max(...this)
    const index = this.indexOf(max)
    this[index] = val
    return val
  }
})

Object.defineProperty(Array.prototype, 'min', {
  get () {
    if (!this.length) {
      return undefined
    }
    
    return Math.min(...this)
  },
  
  set (val) {
    if (!this.length) {
      this.push(val)
      return val
    }
    
    const min = Math.min(...this)
    const index = this.indexOf(min)
    this[index] = val
    return val
  }
})