Javascript constructor - Use an object?

问题

I'm trying to create a new object by using an already made object. This is what I am trying to achieve:

var obj = {"Name" : "Patrick", "Age": 25, "Country": "US"};
document.writeln(JSON.stringify(obj) + "<br />");

function Person(name, age, country) {
    this.name = name;
    this.age = age;
    this.country = country;
}

document.writeln(JSON.stringify(new Person(obj)));

https://jsfiddle.net/dotjz9tb/

As you can see, I am trying to create a new person called Patrick, aged 25, who happens to live in the US. My Person constructor takes a name, an age, and a country as parameters. However, my object has already been created from a previous function, so I would like to do new Person(obj) and it would create a new object based on obj's parameters.

I know I can do new Person(obj.name, obj.age, obj.country) but I would rather pass the constructor an object instead, while still being able to do new Person("Jack", 52, "UK").

Is such thing possible? Right now this is how it's really being created:

new Person(obj, undefined, undefined);
//or
{
    "name": {
        "Name":" Patrick","
         Age":25,
        "Country":"US"
    }
}

Meaning that age and country is set to nothing, while name is set to my object.

回答1:

You have plenty of options here.

For example you could make your Person polymorphic on arguments it takes.

function Person(name, age, country) {
   if(arguments.length === 1 && typeof name === 'object') {
      var data = arguments[0];
      name = data.name; //etc
   } 
   //the rest of ctor code goes here
}

Or BETTER use factory function and keep your constructor code as simple is possible

function copyPerson(obj) {
   return new Person(obj.name, obj.age, obj.country);
}

//or even
Person.copy = function(obj) {
   return new this(obj.name, obj.age, obj.country)
}

回答2:

In general it's better to avoid polymorphic interfaces. They end up being hard to maintain and document and remember.

In this case, I'd change the signature of the constructor to take an object, so

function Person(data) {
  Object.assign(this, data);
}

Now you can call it as

var patrick = new Person({name: 'Patrick', age: 25, country: 'US'});
var patrick2 = new Person(patrick);

回答3:

This is what you could do to support both the input formats:

   function Person(name, age, country) {
        var obj;
        if(typeof(name) === 'object'){
          obj = name;
          name = obj.name;
          age = obj.age;
          country = obj.country;
        }
        this.name = name;
        this.age = age;
        this.country = country;
    }

回答4:

var Person = function(nameOrObj, age, country) {
  if (typeof nameOrObj === 'object') {
    this.name = nameOrObj.name
    this.age = nameOrObj.age
    this.country = nameOrObj.country
  } else {
    this.name = nameOrObj
    this.age = age
    this.country = country
  }
}

来源：https://stackoverflow.com/questions/37520578/javascript-constructor-use-an-object

标签

javascript

constructor