# Proxy

var proxy = new Proxy(target, handler)

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target表示所要拦截的目标对象；
handler用来定制拦截行为；

# get(target, propKey, receiver) 拦截对象属性的读取操作

# set(target, propKey, value, receiver)

# has(target, propKey)

# deleteProperty(target, propKey)

# ownKeys(target)

# getOwnPropertyDescriptor(target, propKey)