Node JS / Javascript: Promise, uncaught exception not being handled by 'reject'

Question

I set up the following to handle queries to a SQLite database. When there are no errors with the query, it performs as expected and all rows are logged to the console.

When I test the functionality by adding a typo to the table name, I get an uncaught exception. I'm not sure why this is the case, and I thought that the exception would be handled by reject(). I'm new to JS and not sure where I'm going wrong here. Any help appreciated.

const sqlite3 = require("sqlite3").verbose();
const dbPath = "db_path";
const db = new sqlite3.Database(dbPath);

const query = (command, method = "all") => {
  return new Promise((resolve, reject) => {
    db[method](command, (error, result) => {
      if (error) {
        reject(error);
      } else {
        resolve(result);
      }
    });
  });
};

async function getResults() {
  const results = await query("SELECT * FROM nonexistant_table");
  console.log(results);
}
getResults();

This is the exception I'm getting:

node:internal/process/promises:391
    triggerUncaughtException(err, true /* fromPromise */);
    ^

Error: SQLITE_ERROR: no such table: set_master1
--> in Database#all('SELECT * FROM set_master1', [Function (anonymous)])
    at D:\test_folder\js_tutorial\main.js:7:15
    at new Promise (<anonymous>)
    at query (D:\test_folder\js_tutorial\main.js:6:10)
    at getResults (D:\test_folder\js_tutorial\main.js:18:25)
    at Object.<anonymous> (D:\test_folder\js_tutorial\main.js:21:1)
    at Module._compile (node:internal/modules/cjs/loader:1469:14)
    at Module._extensions..js (node:internal/modules/cjs/loader:1548:10)
    at Module.load (node:internal/modules/cjs/loader:1288:32)
    at Module._load (node:internal/modules/cjs/loader:1104:12) {
  errno: 1,
  code: 'SQLITE_ERROR',
  __augmented: true
}

Node.js v20.18.0

It is handled by reject() but rejecting a promise throws an error which you don't handle in the getResults() function. Either add try..catch around the function call or if you don't want any errors thrown then use resolve() even when the query fails. — Guy Incognito
– Guy Incognito, Commented Oct 23, 2024 at 15:53
@GuyIncognito thank you it all makes sense now. I hadn't understood that rejecting a promise would throw an error. — Sam WB
– Sam WB, Commented Oct 23, 2024 at 16:00

SubrataG · Accepted Answer · 2024-10-23 16:07:28Z

Since there's no try-catch block around the await query(...) call in getResults, the rejection is not handled,

Your code should be

const sqlite3 = require("sqlite3").verbose();
const dbPath = "db_path";
const db = new sqlite3.Database(dbPath);

const query = (command, method = "all") => {
  return new Promise((resolve, reject) => {
    db[method](command, (error, result) => {
      if (error) {
        reject(error);
      } else {
        resolve(result);
      }
    });
  });
};

async function getResults() {
  try {
    const results = await query("SELECT * FROM nonexistant_table");
    console.log(results);
  } catch (error) {
    // Error is now caught and handled here
    console.error("Error executing query:", error.message);
  }
}

getResults();

Collectives™ on Stack Overflow

Node JS / Javascript: Promise, uncaught exception not being handled by 'reject'

1 Answer 1

Comments

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Related