Javascript: using value in array to access variable

Question

I have multiple variables named for instance "s11" and "s12" etc.

var s11 = 0;
var s12 = 0;

In addition to that, I also have an array containing all the names of these variables.

var wA = new Array("s11", "s12");

The values in the array are added automatically in the script later on, depending on user activity.

My problem is that I would like for example the variable "s11" to ++ every time it occurs as a value in the array. Can this be done?

• Dogbert: Can you use an array instead of the "multiple variables named s11 s12"?
• Chris Bode: Yes, but you'd probably have to write an if statement for every variable that could possibly be incremented. Could you make a second array thats indexed with the field names and increment that instead? eg var fields = {"s11":0,"s12":0};
• Thomas: You mean I can simply input the count into the wA array? Then I would not need the variables.

Answer 1

Using variables, will make your life hard. Here is one approach that does both. Use associative array, like this:

var count = {};
var wA = new Array("s11", "s12");
function updateArray(value) {
 wA.push(value);
 if(! (value in count) ) {
 count[value] = 0;
 }
 count[value]++;
}

Then use it like:

updateArray("s11");
updateArray("s12");

Now count will look like: {s11: 1, s12: 1} & wA will look like: ['s11', 's12']

• Thomas: Seems to be working perfectly! I will just double check everything before pressing solved.
• user405398: @Thomas: yea, also don't forget to +1 ;-)
• Thomas: Yes, it works as beautifully as a sunset on the eastern archipelago of Sweden, with a soft breeze running through your hair!

Answer 2

You could use the eval() function. It runs any code given as argument. For example, to ++ each variable when its name appears in the array, use:

for(variablename in wA){ // or any other way to loop through the array
 eval(variablename + "++");
}

Also, you could use the owner object like an associative array. If the variables are global, just use window.

for(variablename in wA){ // or any other way to loop through the array
 window[variablename]++;
}

Answer 3

If your s variables are global then you could dot he following :

for (var i = wA.length; i--;)
 window[wA[i]] ++;

Answer 4

If they are global variables, you can grab them from the window object using bracket notation:

window[wA[0]]; // 0

Otherwsie, I would recommend using an object instead of variables:

var myVars = {
 s11 : 0,
 s12 : 0
};
myVars[wA[0]]; // 0

The only other way is using eval, which might be dangerous if you're dealing with user input.

Answer 5

If your variables are global you can do as shown below

s11 = 10;
s12 = 12;
var i = 11;
var wA = new Array(window["s" + i++], window["s" + i]);

Otherwise you will have to declare the variables in a scope , for e.g: using this

this.s11 = 10;
this.s12 = 12;
var i = 11;
var wA = new Array(this["s" + i++], this["s" + i]);

Or you can use a loop to push elements

var wA = [];
for(var i=11; i<=12; i++){
 wA.push(this["s" + i]);
}

NOTE: starting and end values of i depends on your requirement and implementation