How the new operator works

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Related issues

• new What does the operator do
• new Simulation Implementation of operators

Answer key points

Constructors Object instances

new Operator by executing a custom constructor or a built-in object constructor , Generate the corresponding object instance .

In depth knowledge

1. new What does the operator do

1. Create a new object in memory .
2. The inside of the new object __proto__ Assigned to the constructor prototype attribute .
3. Will be inside the constructor this Assigned as a new object （ namely this Point to a new object ）.
4. Execute the code inside the constructor （ Add properties to the new object ）.
5. If the constructor returns a non empty object , Returns the object . Otherwise return to this.

2. new Simulation Implementation of operators

function fakeNew() {
  //  Create new objects 
  var obj = Object.create(null);
  var Constructor = [].shift.call(arguments);
  //  Will be the object of  __proto__  Assigned to the constructor  prototype  attribute 
  obj.__proto__ = Constructor.prototype;
  //  Will be inside the constructor  this  Assign as new object 
  var ret = Constructor.apply(obj, arguments);
  //  Return to new object 
  return typeof ret === "object" && ret !== null ? ret : obj;
}

function Group(name, member) {
  this.name = name;
  this.member = member;
}

var group = fakeNew(Group, "hzfe", 17);

Reference material

1. new The operator - MDN
2. The new Operator