js中object的property系列，如何打造一个可编程的setget?

var o={};
var bValue = 1;
Object.defineProperty(o, 'b', {
  get() { return bValue; },
  set(newValue) { bValue = newValue; },
});

var o={};
var bValue = 1;
Object.defineProperty(o, 'b', {
  get: function() { return bValue; },
  set: function(newValue) { bValue = newValue; },
});

var o={};
Object.defineProperty(o, 'b', {
  get: function() { return this.bValue; },
  set: function(newValue) { this.bValue = newValue; },
});

var o={};
var bValue = 1;
Object.defineProperty(o, 'b', {
  writable:false,
  value:'',
  get: function() { return bValue; },
  set: function(newValue) { bValue = newValue; },
});

Error: Invalid property descriptor. Cannot both specify accessors and a value or writable attribute, #<Object>

const object1 = {
    property1:'p1'
};
var _value= "init";
Object.defineProperty(object1, 'property2', {
  //value:"init",
  //writable:true,
  get() { return _value+"_get"; },
  set(newValue) { _value = newValue+"_set"; }
});
console.log(object1.property2);
object1.property2="init2";
console.log(object1.property2);

> "init_get"
> "init2_set_get"