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JavaScript promises, mastering the asynchronous

Magus
37.9K views

Are you really listening? Let's see.

function job() {
    return new Promise(function(resolve, reject) {
        reject();
    });
}

let promise = job();

promise

.then(function() {
    console.log('Success 1');
})

.then(function() {
    console.log('Success 2');
})

.then(function() {
    console.log('Success 3');
})

.catch(function() {
    console.log('Error 1');
})

.then(function() {
    console.log('Success 4');
});
What is the output of the code above ?
function job(state) {
    return new Promise(function(resolve, reject) {
        if (state) {
            resolve('success');
        } else {
            reject('error');
        }
    });
}

let promise = job(true);

promise

.then(function(data) {
    console.log(data);

    return job(false);
})

.catch(function(error) {
    console.log(error);

    return 'Error caught';
})

.then(function(data) {
    console.log(data);

    return job(true);
})

.catch(function(error) {
    console.log(error);
});
What is the output of the code above?
function job(state) {
    return new Promise(function(resolve, reject) {
        if (state) {
            resolve('success');
        } else {
            reject('error');
        }
    });
}

let promise = job(true);

promise

.then(function(data) {
    console.log(data);

    return job(true);
})

.then(function(data) {
    if (data !== 'victory') {
        throw 'Defeat';
    }

    return job(true);
})

.then(function(data) {
    console.log(data);
})

.catch(function(error) {
    console.log(error);

    return job(false);
})

.then(function(data) {
    console.log(data);

    return job(true);
})

.catch(function(error) {
    console.log(error);

    return 'Error caught';
})

.then(function(data) {
    console.log(data);

    return new Error('test');
})

.then(function(data) {
    console.log('Success:', data.message);
})

.catch(function(data) {
    console.log('Error:', data.message);
});
What is the output of the code above?
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