How do you get a static reference to a method of a class in JavaScript?

April 20, 2022

Say I want to pass around a reference to a method of a class in JavaScript:

class Example {
  constructor() {
    this.field = "value"
  }
  exampleMethod() {
    console.log(this.field)
  }
  exampleMethod2() {
    this.field += "."
  }
}

// get references to the methods without having an instance of the object (important detail)
let methods = [Example.exampleMethod, Example.exampleMethod2]  // not correct
let sampledMethod = methods[Math.floor(Math.random()*methods.length)]
let object = new Example()
object.sampledMethod()

Weird example, but say I have more legitimate reasons for wanting these references without an instance of the object. Is there a clean way to do so?

>Solution :

The methods exist on the object’s prototype. To call a detached method on an object instance, use .call or .apply:

class Example {
  constructor() {
    this.field = "value"
  }
  exampleMethod() {
    console.log(this.field)
  }
  exampleMethod2() {
    this.field += "."
  }
}

let methods = [Example.prototype.exampleMethod, Example.prototype.exampleMethod2];
let sampledMethod = methods[Math.floor(Math.random() * methods.length)];

let object = new Example();
console.log(object);
console.log('Calling', sampledMethod);
sampledMethod.call(object);
console.log(object);