Logic in for loop using JavaScript

Question

I am having some problem when trying to perform some calculation inside a for loop using JavaScript:

for (var j = 0; j < count; j++) {
    var attributes;
    if (latlng !== 'Null') {
        attributes = results[j].feature.attributes;
    }                               
    var totalYC = parseInt(attributes["AGE_0_2"] + attributes["AGE_3_4"] + attributes["AGE_5_6"]);      
    var r = {
        pa: attributes["Planning Area Name"],
        sitearea: parseFloat(attributes["SHAPE_Area"] * 0.0001),
        total_pop: parseInt(attributes["TOTAL_POPULATION"]),
        scpr: parseInt(attributes["TOTAL_SCPR"]),
        yc: parseInt(totalYC),
        age_0_2: parseInt(attributes["AGE_0_2"]),
        age_3_4: parseInt(attributes["AGE_3_4"]),
        age_5_6: parseInt(attributes["AGE_5_6"]),        
    };

    r_array.push(r);
}

I want my totalYC to sum up for the total of attributes["AGE_0_2"] + attributes["AGE_3_4"] + attributes["AGE_5_6"] just for once only. Let's say attributes["AGE_0_2"] is 1, attributes["AGE_3_4"] is 2 and attributes["AGE_5_6"] is 3. The totalYC should be 6 but not looping thru the entire for loop and keep on plusing.

Thanks in advance.

Each time through the loop uses a different attributes array (taken from results[j] for different values of j each time). Each pass should create a different 'r' value that gets pushed, each having yc as the total of those values for that particular pass. What are you seeing that's wrong? — Always Learning
– Always Learning, Commented Apr 9, 2014 at 2:18
But the value I am having is way too big. The problem comes from the for loop because it keeps on adding each time — user2424370
– user2424370, Commented Apr 9, 2014 at 2:23
I don't see anything in your code that would keep increasing the value of 'attributes' and thus totalYC. Can you parseInt() each value individually and see if it makes any difference? parseInt(attributes["AGE_0_2"]) + parseInt(attributes["AGE_3_4"]) + parseInt(attributes["AGE_5_6"]); — Ben Wong
– Ben Wong, Commented Apr 9, 2014 at 2:29

jasonscript · Accepted Answer · 2014-04-09 02:35:56Z

You have to parse the items individually before adding them together.

Using your example of

attributes["AGE_0_2"] is 1
attributes["AGE_3_4"] is 2
attributes["AGE_5_6"] is 3

your code

var totalYC = parseInt(attributes["AGE_0_2"] + attributes["AGE_3_4"] + attributes["AGE_5_6"]);

is probably returning 123

If you change to

var totalYC = parseInt(attributes["AGE_0_2"]) + parseInt(attributes["AGE_3_4"]) + parseInt(attributes["AGE_5_6"]);

you should now get 6

EDIT

Because JavaScript doesn't have typed variables it assumes that you are appending strings together.

So when you type attributes["AGE_0_2"] + attributes["AGE_3_4"] + attributes["AGE_5_6"] it is like you are saying "1" + "2" + "3". JavaScript will try to append these values together which returns "123".

Using the ParseInt method tells JavaScript to try and parse these variables as numbers first. JavaScript is smart enough to know that the + operator is therefore a math operator and not an append.

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