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.

Learn more about new: developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… — Felix Kling
– Felix Kling, Commented Mar 4, 2015 at 22:45

jfriend00 · Accepted Answer · 2015-03-04 22:45:16Z

4

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.

edited Mar 4, 2015 at 22:45

answered Mar 4, 2015 at 22:27

jfriend00

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3 Comments

Csteele5 Over a year ago

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 Over a year ago

@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 Over a year ago

I got it working, it was just being finnicky. Thanks for the help!

Michel · Accepted Answer · 2015-03-04 22:47:18Z

0

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.

edited Mar 4, 2015 at 22:47

answered Mar 4, 2015 at 22:28

Michel

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