setting a javascript object property to a variable

Question

How can I set a property of my object to a variable? The variable is equal to a form textfield value. Both obj.property and obj[property] give me a undefined error when I display the mycar object.

function auto(manufacturer,model,engine_size,year,color,price) 
{
    this.manufacturer = manufacturer;
    this.model = model;
    this.engine_size = engine_size;
    this.year = year;
    this.color = color;
    this.price = price;
}

var mycar = new auto();

var a = document.form.num1.value;
mycar.manufacturer = a;
mycar[manufacturer] = a;

sorry. here is all of my code http://jsfiddle.net/vzqjv/

im trying to set my object property to a variable, a, which is equal to a form textfield value after some validation to see if it checks out.

@KhanhTo: But that won't give an error (on the mycar lines), will it? — Qantas 94 Heavy
– Qantas 94 Heavy, Commented Apr 30, 2013 at 3:26
because if "a" is undefined, when he assigned an undefined value to mycar.manufacturer, the mycar.manufacturer will be undefined. — Khanh TO
– Khanh TO, Commented Apr 30, 2013 at 3:28
@KhanhTo - And that is completely legal. That will not cause an undefined error, just an undefined assignment. — Steve
– Steve, Commented Apr 30, 2013 at 3:29

Rick Viscomi · Accepted Answer · 2013-04-30 03:20:20Z

1

mycar.manufacturer = a assigns a to a property of mycar named manufacturer.

mycar[manufacturer] = a assigns a to a property of mycar with the same name as the value of a variable manufacturer. You probably meant mycar["manufacturer"] = a.

answered Apr 30, 2013 at 3:20

Rick Viscomi

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Comments

Steve · Accepted Answer · 2013-04-30 03:23:08Z

1

You haven't declared your variable manufacturer, so it is undefined when you do mycar[manufacturer] = a;. You need to either define it

var a = document.form.num1.value,
    manufacturer = "manufacturer";
mycar.manufacturer = a;
mycar[manufacturer] = a;

or use quotes:

var a = document.form.num1.value;
mycar.manufacturer = a;
mycar["manufacturer"] = a;

answered Apr 30, 2013 at 3:23

Steve

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Comments

Ben McCormick · Accepted Answer · 2013-04-30 03:24:28Z

1

The second notation

mycar[manufacturer] = a;

should be

mycar["manufacturer"] = a;

The first notation should work. Are you modifying mycar in a way that we don't see?

My guess is that the undefined error is actually on this line:

var a = document.form.num1.value;

is that being defined correctly?

edited Apr 30, 2013 at 3:24

answered Apr 30, 2013 at 3:22

Ben McCormick

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1 Comment

doppelgreener Over a year ago

document.form.num1.value; seems to be returning correctly according to dev tools. It's probably just the mycar[manufacturer]!

user650749 · Accepted Answer · 2013-04-30 03:22:43Z

0

You didn't give the definition of the auto. I guess you don't have the manufacturer property in it. Another way is just do

var mycar = {};
var a = document.form.num1.value;
mycar.manufacturer = a;

answered Apr 30, 2013 at 3:22

user650749

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