JavaScript Calculate array of objects

Question

I have some struggles calculating inside a for each function with JavaScript. I have one array of objects that looks like this:

[
    {
        "attribute_operator": "*",
        "attribute_value_price": 3
    },
    {
        "attribute_operator": "+",
        "attribute_value_price": 2
    },
    {
        "attribute_operator": "*",
        "attribute_value_price": 2
    }
]

As you see, every value has operator, and there is a starting price, so the real calculation should look like (if starting price is 6 for example):

6 * 3 + 2 * 2

So the output should be in that case 40.

I know how to do it for sum, but how to implement my operator easily?

tried like:

let total = starting_price.value

        calculate_objects.forEach((a: { attribute_value_price: number; }) => {
          total += a.attribute_value_price;
        });

        console.log(total);

You'll need to parse the operator string and determine which mathematical operation to perform. — Jasen
– Jasen, Commented Mar 8, 2022 at 2:54
Not to nitpick, since the use case is unknown, but the answer to 6 * 3 + 2 * 2 is 22 (18 + 4). The order of operation follows PEMDAS — disinfor
– disinfor, Commented Mar 8, 2022 at 3:13

danh · Accepted Answer · 2022-03-08 02:55:48Z

3

This is a good case for reduce. The starting value is that starting_price, and each turn of the loop applies a little function related to the operand...

const starting_price = 6;
const operations = [{
    "attribute_operator": "*",
    "attribute_value_price": 3
  },
  {
    "attribute_operator": "+",
    "attribute_value_price": 2
  },
  {
    "attribute_operator": "*",
    "attribute_value_price": 2
  }
];

const operators = {
  '*': (a, b) => a * b,
  '+': (a, b) => a + b,
};

const result = operations.reduce((acc, el) => {
  let operator = operators[el.attribute_operator];
  let operand = el.attribute_value_price;
  return operator(acc, operand);
}, starting_price);

console.log(result);

answered Mar 8, 2022 at 2:55

danh

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1 Comment

SARAN SURYA Over a year ago

This is a great answer, it surely allows to create custom operations also.

Elikill58 · Accepted Answer · 2022-03-08 09:05:00Z

-1

You can use string literal with eval function. eval function is useful when you want to calculate an expression.

const obj = [
    {
        "attribute_operator": "*",
        "attribute_value_price": 3
    },
    {
        "attribute_operator": "+",
        "attribute_value_price": 2
    },
    {
        "attribute_operator": "*",
        "attribute_value_price": 2
    }
]
let starting_price = 6;
let total = starting_price;

obj.forEach((a) => {
    total =eval(`${total}${a.attribute_operator}${a.attribute_value_price}`) ;
});

console.log(total);

Warning: Executing JavaScript from a string is an BIG security risk.

With eval(), malicious code can run inside your application without permission.

With eval(), third-party code can see the scope of your application, whitch can lead to possible attacks.

edited Mar 8, 2022 at 9:05

Elikill58

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answered Mar 8, 2022 at 3:10

Yash Vora

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2 Comments

Community Over a year ago

Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center.

SARAN SURYA Over a year ago

This might be an optimal solution, but the answer from @danh is much more clear, and easy for custom implementation

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