promise resolve and reject code example
Example 1: js create a promise
/*
A Promise is a proxy for a value not necessarily known when the promise is created.
It allows you to associate handlers with an asynchronous action's eventual success
value or failure reason.
*/
let promise = new Promise((resolve , reject) => {
fetch("https://myAPI")
.then((res) => {
// successfully got data
resolve(res);
})
.catch((err) => {
// an error occured
reject(err);
});
});
Example 2: 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。${error}`);
})
Example 3: promise javascript
const promiseA = new Promise( (resolutionFunc,rejectionFunc) => {
resolutionFunc(777);
});
// At this point, "promiseA" is already settled.
promiseA.then( (val) => console.log("asynchronous logging has val:",val) );
console.log("immediate logging");
// produces output in this order:
// immediate logging
// asynchronous logging has val: 777
Example 4: promise resolve reject
function testFunction() {
return new Promise(function (resolve, reject) {
setTimeout(function () {
resolve('hello!');
}, 1000);
})
}
testFunction()
.then(function (value) {
console.log(value);
})
.catch(function (error) {
console.log(error);
})
Example 5: promise resolve reject
function testFunction(value) {
return new Promise(function (resoleve, reject) {
setTimeout(function () {
let n = value;
if(n<100){
resoleve("範囲内");
}else{
reject("範囲外");
}
}, 2000);
})
}
testFunction(1000)
.then(function (value) {
console.log(value);
})
.catch(function(error){
console.log(`エラーです。${error}`);
})