What is the best way to implement a Promise Function within a For loop?

Question

What is the best way to implement a Promise Function within a For loop?

Here is a function called sendEmail:

public async sendEmail (log: LogMessage): Promise<void> {
nodemailer.createTestAccount(async () => {
      return ServiceFactory.getSystemService().getNetworkPreferences().then(async (networkPreferences) => {
....

I am looking to incorporate this function into a for loop:

for (const log of logs) {
          const timestamp = moment(log.creationDate)
          const startTime = new Date(Date.now())
          if ((timestamp.diff(startTime)) >= rule.miliSecond && category.includes(log.category)) {

            return this.sendEmail(log)
          }
        }

The issue I am facing is that I cannot remove "return this.sendEmail(log)" since the function returns a Promise. However, the loop only runs once with the first log before terminating. How can I make sure the function is executed within the loop?

typescript for-loop promise

Answer 1

Answer №1

To efficiently handle multiple promises, store them in an array and create a promise that resolves only when all the sendEmail promises have completed.

sendAll() {
    let allMails: Promise<void>[] = [];
    for (const log of logs) {
        const timestamp = moment(log.creationDate)
        const startTime = new Date(Date.now())
        if ((timestamp.diff(startTime)) >= rule.miliSecond && category.includes(log.category)) {

            allMails.push(this.sendEmail(log));
        }
    }
    return Promise.all(allMails);
}

If you prefer to execute the sendEmail functions sequentially, you can utilize async/await to pause execution until one email is sent before proceeding with the next one:

async sendAll(): Promise<void> {
    for (const log of logs) {
        const timestamp = moment(log.creationDate)
        const startTime = new Date(Date.now())
        if ((timestamp.diff(startTime)) >= rule.miliSecond && category.includes(log.category)) {

            await this.sendEmail(log);
        }
    }
}

Answer 2

To efficiently handle multiple promises, store them in an array and create a promise that resolves only when all the sendEmail promises have completed.

sendAll() {
    let allMails: Promise<void>[] = [];
    for (const log of logs) {
        const timestamp = moment(log.creationDate)
        const startTime = new Date(Date.now())
        if ((timestamp.diff(startTime)) >= rule.miliSecond && category.includes(log.category)) {

            allMails.push(this.sendEmail(log));
        }
    }
    return Promise.all(allMails);
}

If you prefer to execute the sendEmail functions sequentially, you can utilize async/await to pause execution until one email is sent before proceeding with the next one:

async sendAll(): Promise<void> {
    for (const log of logs) {
        const timestamp = moment(log.creationDate)
        const startTime = new Date(Date.now())
        if ((timestamp.diff(startTime)) >= rule.miliSecond && category.includes(log.category)) {

            await this.sendEmail(log);
        }
    }
}

What is the best way to implement a Promise Function within a For loop?

Answer №1

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