Trying to workout how to deal with an array

Question

I'm in the process of teaching myself javascript and it looks at though I've hit a road block. As an exercise I am trying to build a tax calculator.

Here is an object I built that contains the tax brackets:

var taxBracket = [
{bracket: 1, from:0, to:18200, percentage :0, amount:0},
{bracket: 2, from:18201, to:37000, percentage :19, over:18200, amount:0},
{bracket: 3, from:37001, to:80000, percentage :32.5, over:37000, amount:3752},
{bracket: 4, from:80001, to:180000, percentage :37, over:80000, amount:17547},
{bracket: 5, from:180001, to:0, percentage :45, over:180000, amount:54547}];

and here is the function that loops through object to find the corresponding tax bracket of y

function returnTax (y){
    for(var x in taxBracket){
    if (y >= taxBracket[x].from && y <= taxBracket[x].to){
        var z = taxBracket[x].amount + ((grossIncome-taxBracket[x].over) * (taxBracket[x].percentage/100));
        return z;   
    }
};

The issue is that if y is over 180000, it errors out as to is 0. Is this only solution to this an else statement repeating the functions of the if statement? Thank for your help!

Unrelated to the problem you asked about, your function uses a `grossIncome` variable that isn't declared in the function. Shouldn't that be `y`? Also, I'd suggest renaming the `y` variable to something more meaningful, like `income` or `grossIncome`. Finally, if you're testing values entered by the user, be careful to ensure they enter an integer (or that you round for them), otherwise if they enter, say, 37000.5 they will have a tax bill of 0. — nnnnnn, Aug 31 '14 at 04:29

Richard Foster · Accepted Answer · 2014-08-31T06:19:22.743

Good job with it so far. Simply using Infinity instead of defaulting to 0 on the final bracket will fix it. I've made a couple of recommendations on your syntax as well, hope it helps.

var taxBracket = [
    {bracket: 1, from: 0, to: 18200, percentage: 0, amount: 0},
    {bracket: 2, from: 18201, to: 37000, percentage: 19, over: 18200, amount: 0},
    {bracket: 3, from: 37001, to: 80000, percentage: 32.5, over: 37000, amount: 3752},
    {bracket: 4, from: 80001, to: 180000, percentage: 37, over: 80000, amount: 17547},

    // Use Infinity instead of 0 for the "to" value of bracket 5
    {bracket: 5, from: 180001, to: Infinity, percentage: 45, over: 180000, amount: 54547}
];

// Variable names like 'x', 'y' and 'z' can cause problems with code readability.
// Descriptive names such as "income", or even "string" or "int" will help you out when you come to review your code later!
function returnTax(y){

    // Using for..in with arrays can cause issues with enumerating over object properties.
    // You don't have to worry about it in this case, but a standard for loop (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for) is better practice.
    for(var x = 0; x < taxBracket.length; x++){

        if(y <= taxBracket[x].to){

            // I find breaking up long calculations into separate variables can make it
            // more readable. More preference than anything else though!
            var amountOver = grossIncome - taxBracket[x].over;
            var percent = taxBracket[x].percentage / 100;
            return taxBracket[x].amount + (amountOver * percent);

        }

    }

}

Note that (assuming contiguous tax brackets) you can simplify the `if` statement because you don't need the `.from` test: `if(y <= taxBracket[x].to){`. — nnnnnn, Aug 31 '14 at 04:23

score 2 · Answer 2 · answered Aug 31 '14 at 02:54

2

You are creating an array literal of object literals. You should loop through arrays with a standard for loop.

answered Aug 31 '14 at 02:54

Antiga

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1

[This is a good suggestion, in general](http://stackoverflow.com/questions/500504/why-is-using-for-in-with-array-iteration-such-a-bad-idea), but doesn't really answer this question. Using a regular `for` loop instead would have no affect on `y <= taxBracket[x].to` being `false` when the `to` is `0`. – Jonathan Lonowski Aug 31 '14 at 03:21

score 1 · Answer 3 · answered Aug 31 '14 at 03:12

1

One solution is to make the last "to" field some very large number.

answered Aug 31 '14 at 03:12

Code-Apprentice

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I had thought of that, but it doesn't really deal with the problem. It looks like infinity is the fix. Thanks – andrew_b Aug 31 '14 at 06:13

score 0 · Answer 4 · edited Aug 31 '14 at 03:10

0

you can use built in function to loop array of object like

yourArray.forEach
( function (arrayItem)
{
var x =
arrayItem.prop1 + 2;
alert(x);
 });

edited Aug 31 '14 at 03:10

Anonymous

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answered Aug 31 '14 at 03:05

A l w a y s S u n n y

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How does this help with what the OP describes as "the issue"? – nnnnnn Aug 31 '14 at 04:06

Trying to workout how to deal with an array

4 Answers4