Static methods aren’t any new idea. Other languages have this for very long time.
If you have experience of other backend languages, this concept will not look very different than other languages.

Basically static methods are useful in classes to define utility functions for all the instances.

class Rectangle {
  constructor(width, height){
    this.width = width;
    this.height = height; 
  }
  static area(rect) {
    return rect.width * rect.height
  }
}

let r = new Rectangle(10, 10);
console.log(Rectangle.area(r)); // 100

Important points to keep in mind

• Static methods are not accessible using this in non-static methods.
• Static methods should not use this as instance is not available. this in static method refers to class not instance.
• You can override static methods.

class Square extends Rectangle {
  constructor(width){
    super(width, width)
  }

  static area(rect) {
    return rect.width * rect.rect
  }
}

let s = new Square(5);
console.log(Rectangle.area(s)); // 25

When use static methods

• If you are writing utility classes and they are not supposed to be changed.
• If the method is not using any instance variable.
• If any operation is not dependent on instance creation.
• If there is some code that can easily be shared by all the instance methods, extract that code into a static method.