promise resolve example

Example 1: promise resolve reject

function testFunction(value) {
    return new Promise(function (resoleve, reject) {
        setTimeout(function () {
            let n = value;
            if (n < 100) {
                resoleve("範囲内");
            } else {
                reject("範囲外");
            }
        }, 2000);
    })
}
 
testFunction(10)
    .then(function (value) {
        console.log(value);
        return testFunction(50);
    })
    .then(function (value) {
        console.log(value);
        return testFunction(150);
    })
    .catch(function (error) {
        console.log(`エラーです。${error}`);
    })

Example 2: what is promise in javascript

Promises make async javascript easier as they are easy to use and write than callbacks. Basically , promise is just an object , that gives us either success of async opertion or failue of async operations

Example 3: promise resolve reject

function testFunction() {
    return new Promise(function (resolve, reject) {
        setTimeout(function () {
            resolve('hello!');
        }, 1000);
    })
}
 
testFunction()
    .then(function (value) {
        console.log(value);
    })
    .catch(function (error) {
        console.log(error);
    })

Example 4: Promise.resolve

var original = Promise.resolve(33);
original.then( val => console.log('origianl', val);
var cast = Promise.resolve(original);
cast.then(function(value) {
  console.log('value: ' + value);
});
console.log('original === cast ? ' + (original === cast));

// logs, in order:
// original === cast ? true
// value: 33