解构对象和默认参数

Question

I have a problem to solve involving default parameters and object destructuring. I have an object 'product' with this shape:

{
     name: "Slip Dress",
     priceInCents: 8800,
     availableSizes: [ 0, 2, 4, 6, 10, 12, 16 ]
   }

Here is my code so far, but I am receiving an error that 'availableSizes' is not iterable. Can someone help me correct this code?

I have tried adjusting the default parameters in my function and I have moved my return statements to no avail.

function checkIfSizeIsAvailable(product = {availableSizes:[]}, size = 0) {
  // let availableSizes = product;
  let foundSize = "";
  for (let sizeCheck of product.availableSizes) {
    if (sizeCheck === size) {
      foundSize = size;
    }
  }
  if (foundSize === ""){
    return false;
  } else {
    return true;
  }
  //for (let i = 0; i < sizes.length; i++) {
  // return false;
}

Answer 1

As VLAZ mentioned in a comment, you can pass an object without an availableSizes field and it'll cause that error.

Destructuring happens when your variables together form an object/array on the left-hand size of the assignment:

function checkIfSizeIsAvailable(product = {availableSizes:[]}, size = 0) {
  // ^ Because of the default parameter, product always exists
  // Now we actually destructure with a default value for missing fields
  const { availableSizes = [] } = product;
}

or more compact:

function checkIfSizeIsAvailable({ availableSizes = [] } = {availableSizes:[]}, size = 0) {

}

Mind that this does not defend against non-array values, or even falsy values. A user can pass { availableSizes: false } and your availableSizes would also be false .