06-ref.js

const targetMap = new WeakMap() // targetMap stores the effects that each object should re-run when it's updated
let activeEffect = null // The active effect running

function track(target, key) {
  if (activeEffect) {
    // <------ Check to see if we have an activeEffect
    // We need to make sure this effect is being tracked.
    let depsMap = targetMap.get(target) // Get the current depsMap for this target
    if (!depsMap) {
      // There is no map.
      targetMap.set(target, (depsMap = new Map())) // Create one
    }
    let dep = depsMap.get(key) // Get the current dependencies (effects) that need to be run when this is set
    if (!dep) {
      // There is no dependencies (effects)
      depsMap.set(key, (dep = new Set())) // Create a new Set
    }
    dep.add(activeEffect) // Add effect to dependency map
  }
}

function trigger(target, key) {
  const depsMap = targetMap.get(target) // Does this object have any properties that have dependencies (effects)
  if (!depsMap) {
    return
  }
  let dep = depsMap.get(key) // If there are dependencies (effects) associated with this
  if (dep) {
    dep.forEach((effect) => {
      // run them all
      effect()
    })
  }
}

function reactive(target) {
  const handler = {
    get(target, key, receiver) {
      let result = Reflect.get(target, key, receiver)
      track(target, key) // If this reactive property (target) is GET inside then track the effect to rerun on SET
      return result
    },
    set(target, key, value, receiver) {
      let oldValue = target[key]
      let result = Reflect.set(target, key, value, receiver)
      if (result && oldValue != value) {
        trigger(target, key) // If this reactive property (target) has effects to rerun on SET, trigger them.
      }
      return result
    },
  }
  return new Proxy(target, handler)
}

function ref(raw) {
  const r = {
    get value() {
      track(r, 'value')
      return raw
    },
    set value(newVal) {
      raw = newVal
      trigger(r, 'value')
    },
  }
  return r
}

// function ref(intialValue) {
//   return reactive({ value: initialValue })
// }

function effect(eff) {
  activeEffect = eff
  activeEffect()
  activeEffect = null
}

let product = reactive({ price: 5, quantity: 2 })
let salePrice = ref(0)
let total = 0

effect(() => {
  salePrice.value = product.price * 0.9
})

effect(() => {
  total = salePrice.value * product.quantity
})

console.log(
  `Before updated quantity total (should be 9) = ${total} salePrice (should be 4.5) = ${salePrice.value}`
)
product.quantity = 3
console.log(
  `After updated quantity total (should be 13.5) = ${total} salePrice (should be 4.5) = ${salePrice.value}`
)
product.price = 10
console.log(
  `After updated price total (should be 27) = ${total} salePrice (should be 9) = ${salePrice.value}`
)