JAVASCRIPT

nodejs promise async

// server.js
 
function square(x) {
  return new Promise(resolve => {
    setTimeout(() => {
      resolve(Math.pow(x, 2));
    }, 2000);
  });
}
 
async function layer(x)
{
  const value = await square(x);
  console.log(value);
}
 
layer(10);

async await for promise nodejs

<script>
  const helperPromise = function () {
    const promise = new Promise(function (resolve, reject) {
      const x = "geeksforgeeks";
      const y = "geeksforgeeks";
      if (x === y) {
        resolve("Strings are same");
      } else {
        reject("Strings are not same");
      }
    });
 
    return promise;
  };
 
  async function demoPromise() {
    try {
      let message = await helperPromise();
      console.log(message);
    } catch (error) {
      console.log("Error: " + error);
    }
  }
 
  demoPromise();
</script>

async promise javascript

await new Promise(resolve => setTimeout(resolve, 1000))

example of promise and async in javascript

// example of promise and async in javascript
// 1) promise: we need to write new keyword to create promise
function withConstructor(num){
  return new Promise((resolve, reject) => {
    if (num === 0){
      resolve('zero');
    } else {
      resolve('not zero');
    }
  });
}

withConstructor(0)
  .then((resolveValue) => {
  console.log(` withConstructor(0) returned a promise which resolved to: ${resolveValue}.`);
});
// Output: withConstructor(0) returned a promise which resolved to: zero.

// 2) async:  we don't need to write new keyword to create promise
async function withAsync(num){
  if (num === 0) {
    return 'zero';
  } else {
    return 'not zero';
  }
}

withAsync(100)
  .then((resolveValue) => {
  console.log(` withAsync(100) returned a promise which resolved to: ${resolveValue}.`);
})

// Output: withAsync(100) returned a promise which resolved to: not zero.

promise async await

async function myFetch() {
  let response = await fetch('coffee.jpg');
  if (!response.ok) {
    throw new Error(`HTTP error! status: ${response.status}`);
  }
  return await response.blob();

}

myFetch().then((blob) => {
  let objectURL = URL.createObjectURL(blob);
  let image = document.createElement('img');
  image.src = objectURL;
  document.body.appendChild(image);
}).catch(e => console.log(e));

javascript promise async

await new Promise(resolve => setTimeout(resolve, 5000));

Javascript async await & Promise

we can only use await keyword before a function that

returns either a promise or is itself async.

Note: we can use async function or function returning
a Promise with .then()

nodejs promise async

// Normal Function
function add(a,b){
  return a + b;
}
// Async Function
async function add(a,b){
  return a + b;
}