Let's define JSON data using Record<> and verify the presence of a specific key

Question

Let's define JSON data using Record<> and verify the presence of a specific key

When my backend sends a JSON object with id strings mapping to data, I make use of the Typescript type Record. Since some ids may not exist, I define it as:

let data: Record<string, number | undefined> = {
    'asdf': 1
};

To process this data and check if a key exists, I do:

const id = 'asdf';
if (id in data) {
    const id_data = data[id];
    console.log(id_data + 1); // compiler warns it might be undefined
}

The compiler provides better support for other patterns. So, I'm unsure if this is the best way to handle my backend response. Any suggestions?

json typescript

Answer 1

Answer №1

It is common to encounter this issue because using id in data alone does not ensure that id_data = data[id] will have a defined value. The key may exist in the object but its corresponding value could still be undefined.

To address this, you must explicitly check the value itself.

const data: Record<string, number | undefined> = {
  "asdo2q" : 253,
  "s398dd" : 132,
}

const id = 'asdf';
const id_data = data[id];
if (id_data !== undefined) {
    console.log(id_data + 1); // now it works
}

Answer 2

It is common to encounter this issue because using id in data alone does not ensure that id_data = data[id] will have a defined value. The key may exist in the object but its corresponding value could still be undefined.

To address this, you must explicitly check the value itself.

const data: Record<string, number | undefined> = {
  "asdo2q" : 253,
  "s398dd" : 132,
}

const id = 'asdf';
const id_data = data[id];
if (id_data !== undefined) {
    console.log(id_data + 1); // now it works
}

Let's define JSON data using Record<> and verify the presence of a specific key

Answer №1

Similar questions

Ways to verify if an item is an Express object?

Reading JSON containing German special characters

What is the reason for the regeneration of the 2D array?

What is the best way to handle null properties when using JsonSerializable::jsonSerialize()?

Python authentication system - Verifying user passwords stored in a JSON database

Utilizing JQueryMobile, JSON, and transferring data to a fresh webpage

Issues encounteted when trying to implement Auth0/Angular2-Jwt in Angular 5 environment

Generating a JSON file from a List in Flutter using GetX package: A step-by-step guide

Typescript: The art of selectively exporting specific types

Tips for utilizing functions in an inline HTML translation pipe

Encountered a Milvus 2 Node.js SDK issue: "Error: TypeError: Class extends value undefined is not a constructor or null"

Enhancing Form Fields Dynamically using AJAX and JSON

How can I execute a HTTP POST request in Node.js using MongoDB and Mongoose?

Create an object of a class with the ability to dynamically determine the file path during

Changing numeric key names within nested JSON structures using Python

Accessing JSON information to retrieve a specific key

What method can we use to verify if an object falls within a specified date range when filtering?

Conditional type/interface attribute typing

Typescript disregarding conditional statements

Utilizing JSON parsing with a variable in Go programming language