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JSON.stringify(list) shows an array of strings, however, Array.isArray(list) is false

I am currently trying to debug the issue in the title.

Here’s some additional information:

  • I am receiving the list from a DynamoDB set.
  • JSON.stringify(list) prints: ["elt1","elt2"]
  • Array.isArray(list) === false
  • list.map is undefined, list.forEach is undefined
const list2 = JSON.parse(JSON.stringify(list))
Array.isArray(list2) === true

I have tried the above hack, and it does solve the issue- but it is definitely not conventional.

Tags:

2

Answers


  1. 0

    You’ve made an erroneous assumption: just because something produces an Array when run through JSON.stringify() does not necessarily mean it in itself is an Array to start. Consider this example:

    class MyClass {
  toJSON() {
    return ['a', 'b'];
  }
}

const list = new MyClass();

console.log(JSON.stringify(list));
console.log(Array.isArray(list));
console.log(list.map);
console.log(list.forEach);

    In other words – it’s entirely possible for a class to override the toJSON() method and fundamentally alter how it is processed by JSON.stringify(). I would suspect what you’re encountering is that list is not really an Array (as you allude) but rather some other type that behaves this way when being stringified.

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  2. 0

    It’s return valid output (list.map is undefined, list.forEach is undefined),t because JSON.stringify() convert into a string and you can’t apply any array function on in it.

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