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General Discussion Create an Array of Objects

Melbourne Hauk
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Melbourne Hauk
Full Stack JavaScript Techdegree Student 2,286 Points
Posted by Melbourne Hauk
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Melbourne Hauk
Full Stack JavaScript Techdegree Student 2,286 Points

Excessive/incorrect decimals in computations of total value

For some reason when logging the total value to the console I get a value with a lot of decimal digits but none of the numbers used to compute were like this. Does anyone know why this might be?

Here is what was logged in the final step: [ 'potato chips', 'pretzel sticks', 'string cheese' ]
87.70000000000002

And here are my array values:

products.push(
  {
    name : 'potato chips',
    inventory : 10,
    unit_price : 4.29
  },
  {
    name : 'pretzel sticks',
    inventory : 10,
    unit_price : 3.49
  },
  {
    name : 'string cheese',
    inventory : 10,
    unit_price : 0.99
  }
)

2 Answers

Steven Parker
Steven Parker
231,269 Points
Steven Parker
Steven Parker
231,269 Points

Because of how numbers are stored, very small errors may occur. One good way to handle this is to format calculation results rounded to a fixed number of decimal places when displaying it.

The ".toFixed" and ".toPrecision" methods can be useful here.

Steven Parker
Steven Parker
231,269 Points
Steven Parker
Steven Parker
231,269 Points

Melbourne Hauk — Glad to help. You can mark a question solved by choosing a "best answer".
And happy coding!

Piotr Manczak
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Piotr Manczak
Front End Web Development Techdegree Graduate 29,363 Points
Piotr Manczak
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Piotr Manczak
Front End Web Development Techdegree Graduate 29,363 Points

So let's say:

function totalValue(array){
    let t = 0;
    array.forEach(i => t += i.unit_price * i.inventory);
    return t.toFixed(2);
}

It isn't perfect but it makes things look good.