Compute numerical values about json-logic-js HOT 5 CLOSED

Can you give me some more context? I've got an app that uses the heck out of JsonLogic for taxes, which I'd assume is similar. In that case the rule (stored in the database, per white-label customer) is something like:

var tax = {
    "name":"Florida State Sales Tax",
    "value_rule":{"*":[
        0.06,
        {"var":"goods"}
    ]}
};

var purchase = {"goods":123.45}

var total = purchase.goods +  jsonLogic.apply(tax.value_rule, purchase);

(That's oversimplifying, there's usually an array of taxes and fees, and there are a bunch of subtotals and applicability that also have to be considered, but this is the gist of it.)

One of the little things I 😍 about this process is that if you need to support a fixed fee, making value_rule a number just works, JsonLogic just passes through primitives that aren't rules.

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Thanks @jwadhams
An example of such a computation would be if the discount depends on various factors such as age of the customer, country, gender, etc (this is completely bogus by the way, the real thing is more complicated).

So maybe if age is between 18 to 30 then you get a 10% discount, 30 to 50 you get 20%.
Plus a 10% if country is USA, etc.
Of course all of it stored in database just like you, white label.

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Assuming you can define and document one big data object for them, like transaction below, your customer could provide a rule like discounts -- in this case the result of that rule is a percentage, which your calling code could use like the console.log commands to show pretty subtotals. (that also puts you in a position to error out if your customer's rule tries to give a 110% discount by mistake)

var jsonLogic = require('json-logic-js');

var transaction = {
    total : 100,
    customer : {
        age : 46,
        country : "US"
    }
};

var discounts = {"+":[
    {"if":[
        {"<=":[ 18, {"var":"customer.age"}, 30 ]},
        0.10,
        {"<=":[ 30, {"var":"customer.age"}, 50 ]},
        0.20,
        0
    ]},
    {"if":[
        {"==":[ {"var":"customer.country"}, "US"]},
        0.10,
        0
    ]}
]};

var discount_pct = jsonLogic.apply(discounts, transaction);

console.log("Subtotal: $", transaction.total);
var discount_amount = transaction.total*discount_pct;
console.log("Discounts: ", discount_pct, "% = $", discount_amount);

console.log("Total: $", transaction.total - discount_amount);

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BTW, if you want to support both fixed discounts ($5 off purchases of $100 or more for example) and percentages, I think you'd have to make your customer include the "multiply percentages by total" in the rule themselves (that's how I actually use this).

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Thanks, that should be enough

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