According to docs, there is no special treatment required for JSONB bind arguments. In practice there is:

• When the argument is a single object, it is bound correctly
• When the argument is an Array, it is necessary to call JSON.stringify on the args.

Here's a test case that reproduces the issue:

const { Client } = require('pg');
const { inspect } = require('util');
async function doIt() {
 const client = new Client();
 console.log('Connecting...');
 await client.connect();
 console.log('Connected');
 const a = [
 {
 the: 'quick',
 brown: 'fox',
 jumps: 'over the',
 lazy: 'dog',
 some: { other: 'object', dilroy: ['hello', 'world'], numpty: new Date() }
 }
 ];
 console.log('Inserting...');
 const result = await client.query(`insert into sb_json(c1) values (1ドル) returning *`, [a]);
 console.log(`result = ${inspect(result, { depth: null })}`);
 console.log('Disconnecting...');
 await client.end();
}
doIt()
 .then(() => console.log('All done'))
 .catch(e => console.log(inspect(e)));

Current documented contract is that no special treatment is required.

Possible solution:

• Document current behavior. This is the less ideal solution, as arguably it is better to be consistent. Never call JSON.stringify on args, or always do so. Not one case for arrays, and on case for single items.
• Inspect the contents of the array. If it contains all primitive types insert for that type. Otherwise call JSON.stringify internally. This operation would run in O(n) time - for a very large array it would be slow.