Creating an array of objects and dynamically instantiating them in a while loop in Javascript

Question

I'm trying to create an array of objects for an assignment in Javascript, but the following doesn't seem to work

var employee = {
employeeId: "",
hoursWorked: 0,
overtimeWorked: 0,
wage: 15
};
var employees = [];
var p = 0;
var i = 0;
while(p != -1){
 p = prompt("please enter employee id#")
 employees[i] = new employee();
 employees[i].employeeId = p;
 i++
}

I've gone through and comment debugged my code and the problem seems to be

employees[i] = new employee();

Whether or not I do this outside the loop, or with any element in the array, I don't seem to be able to instantiate any elements of the array as the employee object.

• Felix Kling: Learn more about new: developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…

Answer 1

You can only use new with a constructor function. So, you need to change your employee variable into a constructor function.

function Employee() {
 this.employeeId = "";
 this.hoursWorked = 0;
 this.overtimeWorked = 0;
 this.wage = 15;
};

Then, you can do:

employees[i] = new Employee();

and get a new employee object each time.

---

In your specific case, I'd suggest allowing the constructor to take an argument too and fixing up your while loop to handle cancel of the user prompt appropriately:

function Employee(id) {
 this.employeeId = id;
 this.hoursWorked = 0;
 this.overtimeWorked = 0;
 this.wage = 15;
};
var employees = [];
var p = 0;
while (true) {
 p = prompt("please enter employee id#");
 if (!p) {
 break;
 }
 employees.push(new Employee(p));
};

Working demo: http://jsfiddle.net/jfriend00/zk7bdfrv/

FYI, your while loop was flawed too because prompt() returns null when cancelled, not -1 and you were using the null value.

• Csteele5: With my code exactly like yours, the page doesn't seem to work. it's not letting me use the this keyword doesn't seem to be working when I use it as you have here. Do I need to do the employee = {}; first and then do function employee(id){}; ?
• jfriend00: @Csteele5 - it seems to work fine for me here: jsfiddle.net/jfriend00/zk7bdfrv . You will have to show us the actual code you're using in the context you're using it to know what is wrong.
• Csteele5: I got it working, it was just being finnicky. Thanks for the help!

Answer 2

Define employee as the following :

function Employee() {
 this.employeeId = "";
 this.hoursWorked = 0;
 this.overtimeWorked = 0;
 this.wage = 15;
};

Then instantiate as :

new Employee();

It is a best practice to name your constructor functions with an uppercase first letter. That way, they differ from other objects and you know you can instantiate them.