How to define optional parameters in Java Script

Question

Here is my object construction,

function Employee(name, dob) {
       this.Name = name;
       this.DateOfBirth = new Date(dob);
   }

Now, I have created an instance for this, like

var emp = new Employee("sample","12/12/12");

Its working fine when i print the output.

But, if i create the object like

var emp = new Employee(name = "sample");

or

var emp = new Employee(dob = "12/12/12");

its not working fine. In both the cases, the DateOfBirth field is invalid.

I need to define an object with optional parameters.

Answer 1

JavaScript does not support named optional parameters.

When you do var emp = new Employee(name = "sample");

You're declaring a name global variable, assigning sample to it and passing that to the new call.

You can use objects to accomplish similar syntax in JS:

var emp = new Employee({name:"sample"}); 

Where the Employee function becomes:

function Employee(options) {
       this.Name = options.name;
       if(options.dob !== undefined){
           this.DateOfBirth = new Date(options.dob);
       }
}

Worth mentioning, in practice, you often don't need an Employee class, and can simply do:

var emp = {name:"sample"};

Or:

var emp = {dob:new Date("12/12/12");}

So unless Employee grows to become a real model (and has more than just two fields) I think that you might want to consider that.

Answer 2

function Employee(params) {
    if (typeof params != "undefined") {
        this.Name = (typeof params.name != "undefined") ? params.name : "";
        this.DateOfBirth = (typeof params.dob != "undefined") ? new Date(params.dob) : null;
    }
}

new Employee({
    name: "John",
    dob: "12/12/12"
});
new Employee({
    name: "John"
});
new Employee({
    dob: "12/12/12"
});

or using simple statements using ||.

function Employee(params) {
    params = params || {};
    this.Name = params.name || "";
    this.DateOfBirth = new Date(params.dob || "");
}