ljharb
define-accessor-property 
Define an accessor property on an object. In an engine without descriptors, in loose mode, when only a getter is provided, nonEnumerable is false, and nonConfigurable is false, wil fall back to assignment - otherwise, it will throw.
The two non* options can also be passed null, which will use the existing state if available.
The loose option will mean that if you attempt to set a nonconfigurable/nonwritable accessor property with set, in an environment without descriptor support, it will fall back to normal assignment (and eagerly evaluate the getter).
Usage
var defineAccessorProperty = require('define-accessor-property');
var assert = require('assert');
var str = 'value';
var strThunk = function () { return str; };
var strSetter = function (v) { str = v; };
var random = function () { return Math.random(); };
var obj = {};
defineAccessorProperty(
obj,
'key',
{
get: strThunk,
set: strSetter,
}
);
defineAccessorProperty(
obj,
'key2',
{
get: random, // at least one of "get" or "set" must be provided
nonConfigurable: true, // optional
nonEnumerable: true, // optional
loose: false, // optional
}
);
assert.deepEqual(
Object.getOwnPropertyDescriptors(obj),
{
key: {
configurable: true,
enumerable: true,
get: strThunk,
set: strSetter,
},
key2: {
configurable: false,
enumerable: false,
get: random,
set: undefined,
},
}
);