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JavaScript - Help me read and understand some of this code Please


If the text gets reformatted, then the link above is a screen shot of the code. My questions: 1) the 'Person' was said to be a constructor. From what I understand, constructors instantiate an object--class / object literal with certain properties and behaviors. How is that a constructor because from what I know constructors are nested within a class. I'm not familiar with the syntax, can you point me to a resource on this ? 2) The for loop within the 'Person'. Can you point me to a resource explaining that syntax ' var key in data'. 3) For confirmation, the 'this' is referring to the instance of the Person object right ? I'm just bewildered by the syntax of the creation of the 'Person' and I don't know whether or not to treat it as an object or a class.

'use strict';

var Person = function (data) { for (var key in data) { this[key] = data[key];
} this.getKeys = function () { return Object.keys(this); } }

var Alena = new Person({ name: 'Alena', role: 'Teacher' });

console.log('Alena\'s Keys:', Alena.getKeys()); // 'this' refers to 'Alena'

var getKeys = Alena.getKeys;

console.log(getKeys()); // 'this' refers to the node process

1 Answer

Steven Parker
Steven Parker
228,025 Points

1.Β The class syntax where you have a method named "constructor" nested inside a class is a recent addition to JavaScript. The example shown here is the classic style where the constructor is created as a function that has the name of the class itself. This should be explained in the class you are taking.

2.Β The loop is a "for...in" type. Here's the MDN reference page for for...in.

3.Β The keyword "this" used in a constructor is a reference to the new object instance being created. There's a workshop here called Understanding "this" in JavaScript you may enjoy.

And "Person" in this example is a class (and also the name of the constructor function for that class). An example of an object would be "Alena".