javascript promise chain
// base case
promise
.then(...)
.then(...)
.then(...)
.catch(...)
//real world
coinflip(10)
.then(betAgain)
.then(betAgain)
.then(betAgain)
.then(result => {
console.log(`OMG, WE DID THIS! TIME TO TAKE ${result} HOME!`);
})
.catch(handleRejection);promise chaining
new Promise(function(resolve, reject) {
setTimeout(() => resolve(1), 1000); // (*)
}).then(function(result) { // (**)
alert(result); // 1
return result * 2;
}).then(function(result) { // (***)
alert(result); // 2
return result * 2;
}).then(function(result) {
alert(result); // 4
return result * 2;
});promises chaining
/* Let's break n STEP-BY-STEP (cpy paste n console u'll have clear view)
1. Promises chaining will allow us to add many async operations
in a sequence way (i.e in order)
2. But like we have callback hell, here our code at the end
will be more difficult to read
3. TIPS : Best options are go with >> {FETCH API, Async/Await}
4. NOTE : Learn promises once, understand no.3 in a easy way, above
both completely relay on Promises concept, makesure u understand them
clearly. */
//EXAMPLE
var result = true;
var learsJS = new Promise((resolve,reject) => {
setTimeout(() => {
if(result){ //if true resolve below case
resolve("This is my 1st resolved case");
}
else{
reject("I need some more time");
}
}, 2000);
}).then(resolvedData1 => {
console.log(resolvedData1); //resolved promise1 - 5th line
return new Promise((resolve) => { // returning another promise2
resolve(`${resolvedData1} -- This is 2nd resolved case`)
});
})
.then(resolvedData2 => {
console.log(resolvedData2); //resolved promise2
return new Promise((resolve) => { // returning another promise3
resolve(` ${resolvedData2} -- This is my 3rd resolved case`)
})
})
.then(resolvedData3 => {
console.log(resolvedData3); //resolved promise3
return new Promise((resolve) => { //returning final promise
resolve(` ${resolvedData3} -- This is my Final resolved case`)
})
})
.then(finalData => console.log(finalData)); //resolved final promiseCopyright © 2021 Codeinu
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