Object.create 方法

Posted 2020-09-11 Hello World

Object.create(proto[, propertiesObject])
The Object.create() method creates a new object with the specified prototype object and properties.
第1个参数是该对象的 prototype, 第2个参数和 Object.defineProperties 第2个参数类似

 

var o;

// create an object with null as prototype
o = Object.create(null);


o = {};
// is equivalent to:
o = Object.create(Object.prototype);

function Constructor() {}
o = new Constructor();
// is equivalent to:
o = Object.create(Constructor.prototype);
// Of course, if there is actual initialization code
// in the Constructor function, 
// the Object.create() cannot reflect it


// Example where we create an object with a couple of
// sample properties. (Note that the second parameter
// maps keys to *property descriptors*.)
o = Object.create(Object.prototype, {
  // foo is a regular ‘value property‘
  foo: {
    writable: true,
    configurable: true,
    value: ‘hello‘
  },
  // bar is a getter-and-setter (accessor) property
  bar: {
    configurable: false,
    get: function() { return 10; },
    set: function(value) {
      console.log(‘Setting `o.bar` to‘, value);
    }
/* with ES5 Accessors our code can look like this
    get function() { return 10; },
    set function(value) {
      console.log(‘Setting `o.bar` to‘, value);
    } */
  }
});


// Create a new object whose prototype is a new, empty
// object and add a single property ‘p‘, with value 42.
o = Object.create({}, { p: { value: 42 } });

// by default properties ARE NOT writable,
// enumerable or configurable:
o.p = 24;
o.p;
// 42

o.q = 12;
for (var prop in o) {
  console.log(prop);
}
// ‘q‘

delete o.p;
// false

// to specify an ES3 property
o2 = Object.create({}, {
  p: {
    value: 42,
    writable: true,
    enumerable: true,
    configurable: true
  }
});

 

Polyfill

if (typeof Object.create != ‘function‘) {
  Object.create = (function(undefined) {
    var Temp = function() {};
    return function (prototype, propertiesObject) {
      if(prototype !== Object(prototype)) {
        throw TypeError(
          ‘Argument must be an object, or null‘
        );
      }
      Temp.prototype = prototype || {};
      var result = new Temp();
      Temp.prototype = null;
      if (propertiesObject !== undefined) {
        Object.defineProperties(result, propertiesObject); 
      } 
      
      // to imitate the case of Object.create(null)
      if(prototype === null) {
         result.__proto__ = null;
      } 
      return result;
    };
  })();
}

 

参考地址:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/create