Update a global variable in a Javascript function without using the variable name

Question

I am working on a replica of an old game I played in High School called Drug Wars. I have global variables that hold the qty of each drug owned. Originally I just used a different function for each buy and sell operation for each drug. Trying to save myself some code and provide for some scale ability I wanted to change it to one function for buying, passing the drugqty, drugprice(done by a different function), and the drugname.

The part I am stuck with is trying to update the drugqty (used locally in the function) to the global variable.

function buy(drugqty, drugprice, drugname)
{
if (money < drugprice)
{
    window.alert("You do not have enough money to do that!")
}
else if(money >= drugprice)
{
var maxdrug = money/drugprice;
var addtoqty;
addtoqty=prompt("How many would you like to purchase? They are $" + drugprice +" a unit. You can afford " + Math.floor(maxdrug) + "." );
if((addtoqty*drugprice)>money)
{
    window.alert("Nice try you need more money to do that!")    
}
else {

drugqty = parseInt(drugqty, 10) + parseInt(addtoqty, 10);
money =  money - (drugprice*addtoqty);
document.getElementById(drugname+"qty").innerHTML=drugqty;
document.getElementById("money").innerHTML=money;

}
}

}

Below is my buy button for one particular drug.

<td><center><button onclick="buy(cocaineqty, cocaine, 'cocaine')">Buy</center></button></center></td>

When the button is pressed it calls the function and executes correctly.

I just need to figure out how to update the global variable cocaineqty with what the local function drugqty creates.

I tried things like

drugname+"qty"=drugqty;

My two thoughts were to parse that information again from where it is displayed or somehow update the global variable in the function(again using it for more than one drug in the future so it can be done dynamically)

<td id="cocaineqty" align="center">0</td>

My first post here but I am more than willing to make changes or correct any mistakes with the post. Thanks for your time!

edit: Updated my code for the correct information based on the checked answer

function buy(drugqty, drugprice, drugname)
{
if (money < drugprice)
{
    window.alert("You do not have enough money to do that!")
}
else if(money >= drugprice)
{
var maxdrug = money/drugprice;
var addtoqty;
addtoqty=prompt("How many would you like to purchase? They are $" + drugprice +" a unit. You can afford " + Math.floor(maxdrug) + "." );
if((addtoqty*drugprice)>money)
{
    window.alert("Nice try you need more money to do that!")    
}
else {

drugqty = parseInt(drugqty, 10) + parseInt(addtoqty, 10);
money =  money - (drugprice*addtoqty);
document.getElementById(drugname+"qty").innerHTML=drugqty;
document.getElementById("money").innerHTML=money;
window[drugname+"qty"]=drugqty;

}
}

Thanks again for all of your assistance!

Welcome to SO! Nice amount of details and code snippets. Keep it up! — Veger
– Veger, Commented Jan 8, 2013 at 8:01

Maurice Butler · Accepted Answer · 2013-01-08 08:12:14Z

1

Firstly they way this im implemented is not awesome. There is a lot that could be done better but Im not going to try to change you implementation here... :)

To do what you want to do, that is access a global variable without knowing its actual name, can be done like this.

window[drugname + "qty"] = drugqty;

This works because

"Global" variable in a browser are actually on the window object
objects in JavaScript are associative arrays. Which in simple terms means you can access its properties via it name as you would in a Key Value pair

answered Jan 8, 2013 at 8:12

Maurice Butler

4142 silver badges9 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

mcfunk Over a year ago

For my poorly implemented idea this was the solution I was looking for. Thank you for your help. I would be curious as to how you would change some of the implementation or maybe just ideas and what to look at correcting.

Community · Accepted Answer · 2017-05-23 12:12:34Z

0

You can use the eval() function for this:

eval(drugname+"qty"=drugqty);

Note: It would be much better to learn about Object Oriented programming. So you can make a Drug class and class instances (objects) of this class to store the particular drug information. It is easy pass around these classes and keep track of the information!

edited May 23, 2017 at 12:12

CommunityBot

11 silver badge

answered Jan 8, 2013 at 7:58

Veger

38k11 gold badges110 silver badges118 bronze badges

3 Comments

mcfunk Over a year ago

OOP, good call looks like Jacco just posted about that I will have to take a look thanks for the response!

Veger Over a year ago

Jacco used an array, it is an 'in between' :)

mcfunk Over a year ago

Thanks for your help, I could not seem to get the eval() to work :(

Jacco · Accepted Answer · 2013-01-08 08:17:15Z

0

You could save all your quantities in a single object and add a property per drug.

var quantities = {};
quantities[drugname + "qty"] = drugqty;

But, if you want to display the results also, it might be easier to leave out the "qty"-part:

var quantities = {};
quantities[drugname] = drugqty;

And for displaying the results:

var html = "<table>";
for (var quantityName in quantities) {
  if (quantities.hasOwnProperty(quantityName)) {
    html += "<tr><td>" + quantityName + "</td>";
    html += "<td id='" + quantityName + "qty' align='center'>" + quantities[quantityName] + "</td></tr>";
  }
}
html += "</table>";

edited Jan 8, 2013 at 8:17

answered Jan 8, 2013 at 7:59

Jacco

3,2721 gold badge22 silver badges30 bronze badges

6 Comments

mcfunk Over a year ago

I will have to dig in to this a bit more but I believe this is where I need to head with it. Thanks for your time and response!

mcfunk Over a year ago

I have a few questions about this one for you, this is making an array, would it be classified as a jagged array? Again I am just learning here but it seems like the size is not defined, and are the locations in the array what are created with the line "quantities[drugname+"qty"] = drugqty" ?

Jacco Over a year ago

Yes, this is classified as a jagged array: stackoverflow.com/questions/5939504/… . Can you clarify the question "are the locations in the array what are created with the line..."? I don't understand what information you are looking for.

mcfunk Over a year ago

I was just thinking a bit too hard about it I suppose, but I was just wondering if the information in the bracket "[drugname+"qty"]" was the index in the array. Possibly allowing me to set the quantities and ref them by that notation. There is so much information out there that I just confuse myself sometimes trying to incorporate it all. Sorry if this sound more confusing, but thanks again for your help!

Evan Davis Over a year ago

@mcfunk Sounds like you need to read up on Objects and Arrays in JavaScript; you seem to be missing some fundamental knowledge.

|

Collectives™ on Stack Overflow

Update a global variable in a Javascript function without using the variable name

3 Answers 3

1 Comment

3 Comments

6 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

3 Comments

6 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related