How can an async function await the callback of an inner async function?

Question

I have an async function that must return when the callback of an inner async function returns. I cannot await that inner function because it does not return a promise. I've tried specifying await in passing the callback but that does not do the trick. As such:

async getPublicKey(): Promise<string> {

    const callback = async (err: any, key: any) => {
      if (!err) this.publicKey = key.result;
      else console.error(err);
    };

    this.web3js.currentProvider.sendAsync({
      jsonrpc: '2.0',
      method: 'eth_getEncryptionPublicKey',
      params: [this.account],
      from: this.account,
    }, callback);

    return this.publicKey
  }

Here, the goal is to return key.result of the callback function. However, we cannot await that callback and the sendAsync function returns immediately (cannot await it).

look into util.promisify

georg
– georg

2021-07-14 06:20:33 +00:00
Commented Jul 14, 2021 at 6:20 — georg
– georg, Commented Jul 14, 2021 at 6:20

Mark Dreyer · Accepted Answer · 2021-07-14 03:43:13Z

2

You'll want to wrap the callback in a new Promise and return the resolve or reject. This way, you can await your call to await getPublicKey() and it will not resolve until the callback is done.

async getPublicKey(): Promise<string> => {
  return new Promise((resolve, reject) => {
    const callback = async (err: any, key: any) => {
      if (!err) {
          resolve(key.result);
      }
      else {
        reject(err);
      }
    };

    this.web3js.currentProvider.sendAsync({
      jsonrpc: '2.0',
      method: 'eth_getEncryptionPublicKey',
      params: [this.account],
      from: this.account,
    }, callback);

    })
  })
}

answered Jul 14, 2021 at 3:43

Mark Dreyer

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