JS promises

Question 1

How to write a promise

Answer 1

const doWork = new Promise((resolve,reject)=>{
    const a = 1;
    if(a === 1){
        setTimeout(()=>{
            resolve([3,4,5])
        },5000)
    }else{
        setTimeout(()=>{
            reject("Oops")
        },5000)
    }

});

doWork.then((result)=>{
    console.log(result)
}).catch((error)=>{
    console.log(error)
});

Question 2

When does a promise stop running?

Answer 2

When either resolve or reject is called. resolve and reject acts like a return statement

Question 3

How do promises work?

Answer 3

When a promise is called, it is considered pending. Once the pending promise resolves it is considered fullfilled. When it is not resolved it is considered rejected.

Question 4

What is promise chaining?

Answer 4

Chaining multiple promises together

Avoids callback hell or nested and duplicate code

Question 5

How to chain promises?

Answer 5

const sum = (x,y)=>{
    return new Promise((resolve,reject)=>{
        setTimeout(()=>{
            resolve(x + y)
        },3000)
    })
};

sum(5,5).then((result)=>{
    return sum(result,5)
}).then((result)=>{
    return sum(result,5)
}).then((result)=>{
    console.log(result)
}).catch(e=>{
    console.log(e)
});

Question 6

What is Async/Await?

Answer 6

A tool that makes it easier to work with promises. It provides a syntactical advantage, making code more readible, by avoiding promise chaining, and it keeps all variables within the same scope, which makes it easier to access their values