use a variable as an object reference

Question

I am having some trouble trying to assign a variable as an object reference name.

var roomName = 'room_'  + $(this).data("room-id");

    console.log("roomName: " + roomName);

    beds_required_obj.roomName.single_beds_required = parseInt($(this).val());

My console.log reports this: "roomName: room_1" as expected

But I keep getting an error: "TypeError: beds_required_obj.roomName is undefined"

I can use the variable when assigning it as an array:

single_beds_required['room ' + $(this).data("room-id")] = parseInt($(this).val());

But in this case my object is messy and will require extra processing to pull it into a tidy format server side.

How do I use a variable (inside a function) to create a new obj sub group inside a global object?

You almost have it. Use `beds_required_obj[roomName].single_beds_required = ...` — Matt Way, May 31 '16 at 11:12
@Matt Wey.... Yes I had tried that. Returns this error: TypeError: beds_required_obj[roomName] is undefined — Nick, May 31 '16 at 11:13
@Adder - var beds_required_obj = {}; already declared prior to the function in the global scope. — Nick, May 31 '16 at 11:27

score 1 · Accepted Answer · answered May 31 '16 at 11:28

var beds_required_obj = {};

var roomName = 'room_'  + $(this).data("room-id");

console.log("roomName: " + roomName);

if(!beds_required_obj[roomName]) beds_required_obj[roomName] = {};
beds_required_obj[roomName].single_beds_required = parseInt($(this).val());

score 1 · Answer 2 · answered Jun 01 '16 at 01:16

Generally the errors you receive in the console do not lie. So let's break your object down, and see what could possibly cause the error.

var roomName = 'room_'  + $(this).data('room-id');
beds_required_obj.roomName.single_beds_required = ...

Now the code above firstly assumes that beds_required_obj is an object that exists. We can see by the comments that this is indeed true, as you used:

var beds_required_obj = {};

Now because this object exists, you can call beds_required_obj.anything_here, and it will be valid code. However, the child you attempt to access may not exist.

Next you have written beds_required_obj.roomName. Now this is attempting to access a child object named 'roomName', not 'room_id'. In order to access the dynamic name that you have stored in the roomName variable, you need to use square brackets. So:

beds_required_obj[roomName]

This will return the child object of the dynamically created room name.

Now depending on what roomName actually is (it might be 'room_123' for example), this child object also might not exist. If it does not exist, then any attempt to access a child of this object will return your error. For example, look at the code below:

var beds_required_obj = []; // create an empty object
var roomName = 'room_1234'; // the name of our room

// this line below will throw an error because the room_1234 child object does not exist
beds_required_obj[roomName].single_beds_required = 2;

What is happening is that you are trying to access single_beds_required as a child of an undefined object. To make this work, you would need to change the code above to include an extra line:

var beds_required_obj = []; // create an empty object
var roomName = 'room_1234'; // the name of our room

// now create the room child object
beds_required_obj[roomName] = {};
// now this line will work, as the room is a valid object that can have children assigned to it.
beds_required_obj[roomName].single_beds_required = 2;

Note: If you want to do something like this with more readable code (imo), then I would use:

breds_required_obj[roomName] = {
    single_beds_required: 2
};

use a variable as an object reference

2 Answers2