Javascript Promise: managing the flow of execution

Question

Javascript Promise: managing the flow of execution

There are a series of tasks that I need to accomplish using an API. It's crucial that these functions are executed sequentially. Each of the functions mentioned below returns a valid promise.

a(analyticsConfig._listConfig)
    .then(function() {
        return b(listName, analyticsConfig._fieldConfig);
    })
    .then(function() {
        return c(listName)
    })
    .then(function() {
        return d(analyticsConfig._roleConfig);
    })

I wish there was a way to use something like

a.then(b(listName, analyticsConfig._fieldConfig))

, but as you might already realize, this approach won't work.

Can anyone suggest an alternative method to achieve this?

javascript promise chaining

Answer 1

Answer №1

For this method to work, `b` must return a function that in turn returns a promise. It is essential to always provide a function as the callback for `then` - there are no shortcuts around that rule. However, there are numerous ways to create one.

If we set aside techniques like partial application (using `bind`) and currying, your options for cleaner syntax include ES8's `async`/`await`:

(async function() {
    await a(analyticsConfig._listConfig);
    await b(listName, analyticsConfig._fieldConfig);
    await c(listName);
    await d(analyticsConfig._roleConfig);
})();

Alternatively, you can use ES6 arrow functions:

a(analyticsConfig._listConfig)
.then(() => b(listName, analyticsConfig._fieldConfig))
.then(() => c(listName))
.then(() => d(analyticsConfig._roleConfig))

Answer 2

For this method to work, `b` must return a function that in turn returns a promise. It is essential to always provide a function as the callback for `then` - there are no shortcuts around that rule. However, there are numerous ways to create one.

If we set aside techniques like partial application (using `bind`) and currying, your options for cleaner syntax include ES8's `async`/`await`:

(async function() {
    await a(analyticsConfig._listConfig);
    await b(listName, analyticsConfig._fieldConfig);
    await c(listName);
    await d(analyticsConfig._roleConfig);
})();

Alternatively, you can use ES6 arrow functions:

a(analyticsConfig._listConfig)
.then(() => b(listName, analyticsConfig._fieldConfig))
.then(() => c(listName))
.then(() => d(analyticsConfig._roleConfig))

Answer 3

Answer №2

If you prefer, the code can be written like this:

a.then(b.bind(null, listName, analyticsConfig._fieldConfig))

Alternatively, if you are using babel to transpile your code or targeting a version of node greater than v4, you can use:

a.then(() => b(listName, analyticsConfig._fieldConfig))

Answer 4

If you prefer, the code can be written like this:

a.then(b.bind(null, listName, analyticsConfig._fieldConfig))

Alternatively, if you are using babel to transpile your code or targeting a version of node greater than v4, you can use:

a.then(() => b(listName, analyticsConfig._fieldConfig))

Answer 5

Answer №3

To link it together, you can use the following method:

a.then(b.bind(context,listName,analyticsConfig._fieldConfig))

Make sure to assign the appropriate context to it.

As mentioned in the documentation:

The bind() function generates a new function that, upon invocation, sets its this keyword to the provided value, along with a specified order of arguments preceding any additional ones given at call time.

Answer 6

To link it together, you can use the following method:

a.then(b.bind(context,listName,analyticsConfig._fieldConfig))

Make sure to assign the appropriate context to it.

As mentioned in the documentation:

The bind() function generates a new function that, upon invocation, sets its this keyword to the provided value, along with a specified order of arguments preceding any additional ones given at call time.

Answer 7

Answer №4

Here is an example using async/await:

function apple() {
    console.log('Picking Apple...');
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            resolve('Hello Apple!');
        }, 1000);
    });
}

function banana() {
    console.log('Picking Banana...');
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            resolve('Hello Banana!');
        }, 1000);
    });
}

function cherry() {
    console.log('Picking Cherry...');
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            resolve('Hello Cherry!');
        }, 1000);
    });
}

function dateFruit() {
    console.log('Picking Date Fruit...');
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            resolve('Hello Date Fruit!');
        }, 1000);
    });
}

async function getFruits() {
    await apple();
    await banana();
    await cherry();
    await dateFruit();
    console.log('Fruits Picked');
}

Answer 8

Here is an example using async/await:

function apple() {
    console.log('Picking Apple...');
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            resolve('Hello Apple!');
        }, 1000);
    });
}

function banana() {
    console.log('Picking Banana...');
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            resolve('Hello Banana!');
        }, 1000);
    });
}

function cherry() {
    console.log('Picking Cherry...');
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            resolve('Hello Cherry!');
        }, 1000);
    });
}

function dateFruit() {
    console.log('Picking Date Fruit...');
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            resolve('Hello Date Fruit!');
        }, 1000);
    });
}

async function getFruits() {
    await apple();
    await banana();
    await cherry();
    await dateFruit();
    console.log('Fruits Picked');
}

Javascript Promise: managing the flow of execution

Answer №1

Answer №2

Answer №3

Answer №4

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