JavaScript allows developers to define custom objects beyond built - in methods and classes. There are three primary syntaxes for creating custom objects:

1. Using the Built - in Object Constructor

To create an object with the system - provided Object constructor, you can do the following:

// Instantiate an object
let user = new Object();
// Add properties to the object
user.username = "Li Si";
user.age = 28;
user.gender = "Female";
// Add a method to the object
user.play = function (game) {
    console.log(this.username + " is playing " + game);
};

// Access object properties
console.log(user.username);
console.log(user.age);
console.log(user.gender);
// Call the object's method
user.play("Chess");

2. Using a Custom Cnostructor Function

You can also create a custom cosntructor function to generate objects:

// Define a constructor function
function Student(sName, sGrade) {
    this.studentName = sName;
    this.grade = sGrade;

    this.study = function (subject) {
        console.log(this.grade + " - grade student " + this.studentName + " is studying " + subject);
    };
}

let s1 = new Student("Wang Wu", 5);
// Access object properties
console.log(s1.studentName);
console.log(s1.grade);
// Call the object's method
s1.study("Math");

3. Using Object Literal (JSON - like) Syntax

The object literal syntax (similar to JSON format) is a concise way to create objects:

/*
Object literal format:
let objectName = {
    propertyName: propertyValue,
    methodName: function() { ... }
};
*/
let profile = {
    fullName: "Xiao Hong",
    gender: "Female",
    age: 12,
    read: function (book) {
        console.log(this.age + " - year - old " + this.gender + " " + this.fullName + " is reading " + book);
    }
};

// Access object properties
console.log(profile.fullName);
console.log(profile.gender);
console.log(profile.age);
// Call the object's method
profile.read("Fairy Tales");