Default value for options object in class constructor

Question

I\'ve created a class and I would like to set some default options for values in case the user does not supply any arguments. I recently went from a constructor that took mu

Answer 1

Make sure you have a default for the object itself.

module.exports = class User {
    constructor(options) {
        options = options || {}
        this.name = options.name || "Joe";
        this.age = options.age || 47;
    }
}

Answer 2

You could either set a default value for options, i.e {}.

class User {
    constructor(options = {}) {
        this.name = options.name || "Joe";
        this.age = options.age || 47;
    }
}

or first check for options to be truthy and then access the value.

class User {
    constructor(options) {
        this.name = options && options.name || "Joe";
        this.age = options && options.age || 47;
    }
}

Answer 3

If you want to change to a configuration pattern, you can still keep your default parameter syntax:

module.exports = class User {
    constructor({ name = "Joe", age = 47 } = {}) {
        this.name = name;
        this.age = age;
    }
}

const User = require("./user");

const user = new User(); // Defaults to "Joe" and 47

Answer 4

You actually just need a oneliner:

const defaultUser = {
  name: "Joe",
  age: 47
};

module.exports = class User {
  constructor(options) {
     Object.assign(this, defaultUser,  options)
  }
}