Javascript function which is not working

Question

Im learning javascript and run into this problem where I want to combine objects and functions. I have the following which, according to me, should lead to 65 - the age I inserted. I get nothing however.

Any thoughts on what Im doing wrong?

<script type="text/javascript">
function person(name, age) {
this.name = name;
this.age = age;
this.yearsUntilRetire = yearsLeft;
}
function yearsLeft {
var numYears = 65 - this.age;
return numYears;
}
var Marc = new person("Marc", 23);
document.write(Marc.yearsUntilRetire());
</script> 

• Johan: Tip: Add the function to the person prototype for improved performance when creating multiple instances
• Bergi: The casing of your variable names should be backwards: var marc = new Person()

Answer 1

You're just missing parenthesis in the function declaration :

function yearsLeft() {

To fix this kind of errors, you must look at the errors in the console. The line where the syntax error happens is shown.

Recommended reading : Chrome Developer Tools

Answer 2

You forgot () in the yearsLeft declaration!

<script type="text/javascript">
function person(name, age) {
this.name = name;
this.age = age;
this.yearsUntilRetire = yearsLeft;
}
function yearsLeft() {
var numYears = 65 - this.age;
return numYears;
}
var Marc = new person("Marc", 23);
document.write(Marc.yearsUntilRetire());

Answer 3

There could be two errors, if you look at your console, it could be that you are missing () immediately after yearsleft function declaration. and you are trying to write out Marc.yearsUntilRetire() instead of Marc.yearsUntilRetire. I think yearsUntilRetire is a variable that takes the number of years returned from yearsLeft and not a function.

<script type="text/javascript">
function person(name, age) {
this.name = name;
this.age = age;
this.yearsUntilRetire = yearsLeft;
}
function yearsLeft {
var numYears = 65 - this.age;
return numYears;
}
var Marc = new person("Marc", 23);
document.write(Marc.yearsUntilRetire());
</script>