decrator

function log(target) {

console.log(Object.getOwnPropertyDescriptor(target.prototype));  // undefined  这里打印 ？？？？？？

const desc = Object.getOwnPropertyDescriptor(target.prototype);

for (const key of Object.keys(desc)) {

if (key === 'constructor') {

continue;

}

const func = desc[key].value;

if ('function' === typeof func) {

Object.defineProperty(target.prototype, key, {

value(...args) {

console.log('before', key);

const ret = func.apply(this, args);

console.log('after', key);

return ret;

}

})

}

}

}

@log

class Numberic {

PI = 3.1415926;

add (...nums) {

return nums.reduce((p, n) => ( p + n ), 0)

}

}

new Numberic(1, 2);