SOURCE

function observer(target) {
    if (typeof target !== 'object' || target === 'null') return target

    if (Array.isArray(target)) {
        target.__ptoto__ = a
    }

    for (key in target) {
        defineReactive(target, key, target[key])
    }
}

const arr = Array.prototype
const a = Object.create(arr)
['push', 'pop', 'unshift', 'shift'].forEach(methodName => {
    a[methodName] = function() {
        updateView()
        arr[methodName].call(this, ...arguments)
    }
})


function defineReactive(target, key, value) {
    observer(value)
    Object.defineProperty(target, key, {
        get: function() {
            return value
        },
        set: function(newVal) {
            if (newValue !== value) {
                value = newValue
                updateView()
            }
        }
    })
}

function updateView() {
    
}