如何解决错误，filter() 不是函数

Question

Here is what I tried. Also order is part of a query so this works, I am just not posting the rest of the code so it doesn't get messy. I was getting errors on the paymentsResults[i].filter() saying it is not function . Anyways, if there is a better way to write it, please let me know. Appreciate it.

 const getCatType = order => {
  if (
    order.type === "Invoice" ||
    order.type === "One-time" ||
    order.type === "Free"

  ) {
    return "Once";
  } else if (order.type === "Semester") {
    return "Recurring";
  }
};

for (let i = 0; i < paymentsResults.length; i++) {
const paymentsOnce = paymentsResults[i].filter(o => getCatType(o) === "Once");
} 

Answer 1

I assume you are confused with what filter() is actually supposed to do.

filter() is an Array-Function iterating over the given Array and returning the objects that fit the filter-conditions defined in the callback function.

Therefore you don't need the for-Loop to get into each Item of your array, but simply call your filter-function on the array itself.

This only applies if you have an Array of Objects with the key type in paymentsResults. Sadly you didn't provide your origin data-structure. If it is not like I assumed, then please comment down below, what your data structure looks like.

for (let i = 0; i < paymentsResults.length; i++) {
const paymentsOnce = paymentsResults[i].filter(o => getCatType(o) === "Once");
} 

Will become:

// ONLY GIVEN IF YOUR STRUCTURE LOOKS LIKE 
// paymentsResults = [{type: 'Thing'}, {type: 'Thing'}, ...];
const paymentsOnce = paymentsResults.filter(o => getCatType(o) === "Once");

Answer 2

Using a switch would be more useful. And then all you need to do it filter out the objects where they match - no need for an additional loop.

 function getCatType(order) { switch(order.type) { case 'Invoice': case 'One-time': case 'Free': return 'Once'; case 'Semester': return 'Recurring'; default: return null; } } const paymentsResults = [ { type: 'Invoice', id: 1 }, { type: 'Semester', id: 2 }, { type: 'Free', id: 3 }, { type: 'One-time', id: 4 } ]; function typeOfPayment(type) { return paymentsResults.filter(order => { return getCatType(order) === type; }); } console.log(typeOfPayment('Once')); console.log(typeOfPayment('Recurring'));

Answer 3

You can use reduce and also you can check for the types you need directly in the reduce cb, mix this with a regex and you can extract what ever types of orders you want by creating a simple array with the types you need. Assuming your paymentsResults are something like this array you can do this:

 const paymentsResults = [ { order: { type: 'Invoice', total: 10 }, price: 2 }, { order: { type: 'One-time', total: 11 } }, { order: { type: 'Free', total: 12 } }, { order: { type: 'Semester', total: 13 } }, ]; let extract = ['Invoice', 'One-time', 'Free']; const regex = new RegExp(extract.join('|'), 'i'); let paymentsOnce = paymentsResults.reduce((acc, obj) => { if (regex.test(obj.order.type)) acc.push(obj); return acc; }, []); console.log(paymentsOnce);