JavaScript, I promise that I will stay with you, forever!

promise.js

let a = () => new Promise(function (resolve, reject) {
    setTimeout(() => resolve("pass"), 3000);
}).then((res) => { console.log("console outcome promise A after 3 secs"); return "As I promised, I'm here! " + res; })

let b = () => new Promise(function (resolve, reject) {
    setTimeout(() => resolve("pass"), 5000);
}).then((res) => { console.log("console outcome promise B after 5 secs", res); return Promise.resolve("I'm resolved!") })

let c = () => new Promise(function (resolve, reject) {
    setTimeout(() => reject("fail"), 7000);
}).catch((err) => { console.log("console outcome promise C after 7 secs", err); return Promise.reject("I'm rejected!") })

let d = () => new Promise(function (resolve, reject) {
    setTimeout(() => reject("fail"), 0);
}).catch((err) => { console.log("console outcome promise D after 0 sec", err); return Promise.reject("I'm rejected immediately!") })


let execAll = () => Promise.allSettled([a(), b(), c()]).then((res) => { console.log("All promises", res) })


let execAllWithHoldPromises = () => Promise.allSettled(promises).then((res) => { console.log("All promises as input pass by let variable", res) })

// promise will return and executed only function is called
console.log(a,
    execAll,
    execAllWithHoldPromises
)
// Can I return the any value apart from Promise.resolve or Promise.reject?
a()

// Let's confirmed that Promise.allSettled really return after 7 secs, even after promise A completed after 3 secs
execAll()

// check outcome of `[a(), b(), c()]`, it seems promise get evaluated immediately 
let promises = [a(), b(), c()];

// check outcome of `let promises = [a(), b(), c()]`, and use it as input for Promise.allSettled [tip: global execution context]
promises = [a(), b(), c()]; execAllWithHoldPromises()

// check outcome of `let promises = [a(), b(), c(), d()]`, and use it as input for Promise.allSettled [tip: global execution context]
promises = [a(), b(), c(), d()];
// after 10 secs, execute the following command
execAllWithHoldPromises()
// Outcome: you will see the uncaught promise exception first time, then after above command execution error will disappeared 

// Another example with sleep function
let quickNap = (i) => new Promise((resolve, reject) => setTimeout(() => resolve(`Slept for ${i} seconds`), i * 1000))

let users = [1, 3, 5]
users.map(quickNap)

let quickNap = async (i) => new Promise((resolve, reject) => setTimeout(() => { console.log(`Slept for ${i} seconds`); resolve(`Slept for ${i} seconds`) }, i * 1000))

let users = [1, 7, 5]
Promise.allSettled(users.map(await quickNap)).then((res) => console.log(res))


let quickNap = (i) => new Promise(resolve => setTimeout(() => { console.log(`Slept for ${i} seconds`); return resolve(`reSlept for ${i} seconds`) }, i * 1000))

let users = [1, 7, 5]

// for vs forEach vs map
await users.map(await quickNap);
await users.forEach(async i => { console.log(`Seq for ${i} seconds`); await quickNap(i) });
for (let i = 0; i < 3; i++) { await quickNap(users[i]) }

// When you don't resolve your promise in the `.then` block, output always returns `undefined`
let quickNap = (i) => new Promise((resolve, reject) => setTimeout(() => { console.log(`Slept for ${i} seconds`); resolve(`Slept for ${i} seconds`) }, i * 1000))
    .then((r) => console.log(`Slept for ${i} seconds`, r))

let users = [1, 7, 5]
Promise.allSettled(users.map(quickNap)).then((res) => console.log("hmm...", res))

// When you don resolve your promise without `.then` block, output always returns resolved data
let quickNap = (i) => new Promise((resolve, reject) => setTimeout(() => { console.log(`Slept for ${i} seconds`); resolve(`Slept for ${i} seconds`) }, i * 1000))
let users = [1, 7, 5]
Promise.allSettled(users.map(quickNap)).then((res) => console.log("hmm...", res))

// quickest way to check how allSettled work with API, fetch API itself returns the promise, not promise wrapper required
// Following example will failed to get outcome
quickNap = (i) => new Promise(() => fetch('https://api.thecatapi.com/v1/images/search'))
Promise.allSettled(users.map(quickNap)).then((res) => console.log(res))

// following one is working example, but strangely it returns promise object
quickNap = (i) => fetch('https://api.thecatapi.com/v1/images/search')
Promise.allSettled(users.map(quickNap)).then((res) => console.log(res))

// following one is working example, in order to pull out the i need to resolve another promise that is `response.json()`
quickNap = (i) => fetch('https://api.thecatapi.com/v1/images/search')
Promise.allSettled(users.map(quickNap)).then(async (res) => console.log("------------", await res[0].value.json()))

// following one is working example, to simplify it further checking followng example
quickNap = (i) => fetch('https://api.thecatapi.com/v1/images/search').then(response => response.json())
Promise.allSettled(users.map(quickNap)).then(async (res) => console.log("------------", res))

// nested example of `allSettled` where main promise is dependant of following `allSettled` multiple promises 
quickNap = (i) => fetch('https://api.thecatapi.com/v1/images/search').then(response => response.json())
quickNapAllPromises = () => Promise.allSettled(users.map(quickNap)).then((res) => { console.log("------------", res); return res })
execAll = () => Promise.allSettled([a(), b(), c(), quickNapAllPromises()]).then((res) => { console.log("All promises", res) })
execAll()

//Does catch block handles the rejects?
try{
    await c()
}
catch(e){
    console.log("eeeeeeeee-----------",e)
}