JavaScript Classes Class Constructor


The fundamental part of most classes is its constructor, which sets up each instance's initial state and handles any parameters that were passed when calling new.

It's defined in a class block as though you're defining a method named constructor, though it's actually handled as a special case.

class MyClass {
    constructor(option) {
        console.log(`Creating instance using ${option} option.`);
        this.option = option;

Example usage:

const foo = new MyClass('speedy'); // logs: "Creating instance using speedy option"

A small thing to note is that a class constructor cannot be made static via the static keyword, as described below for other methods.