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The JavaScript Interview Handbook: 100+ Interview Questions

Solution Review: Counting Animals

Explore how static methods and variables work in JavaScript's object-oriented programming by reviewing a solution to counting animals. Understand the significance of defining static properties on the class itself rather than on instances. Gain clarity on how to properly manage class-level data to avoid common errors like NaN, and learn two approaches to declare static variables within a class.

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Solution

Node.js
class Animal {
  constructor() {}
  static count = 0;
  static increaseCount() {
    this.count += 1;
  }
  static getCount() {
    return this.count;
  }
}
function test(){
  Animal.increaseCount(); 
  console.log(Animal.getCount()); 
}
test()

Explanation

This challenge is quite simple if you have a sound understanding of static methods and variables. Static properties are assigned to the class instead of its prototype. This is similar to assigning a property directly to a class. For example, the static method static getCount

static getCount() {
    return this.count;
}

is similar to

Animal.getCount = function(){
    return this.count;
}

These functions are used by the ...