Node.js Design Patterns/

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The Callback Pattern: Synchronous vs. Asynchronous (II)

The Callback Pattern: Synchronous vs. Asynchronous (II)

Learn about synchronous APIs and asynchronicity with deferred execution.

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Using synchronous APIs

The lesson to learn from the unleashing Zalgo example is that it is imperative for an API to clearly define its nature: either synchronous or asynchronous.

One possible fix for our inconsistentRead() function is to make it completely synchronous. This is possible because Node.js provides a set of synchronous direct style APIs for most basic I/O operations. For example, we can use the fs.readFileSync() function in place of its asynchronous counterpart. The code would become as follows:

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main.js
package.json
data.txt
import { readFileSync } from 'fs'
const cache = new Map()
function consistentReadSync (filename) {
  if (cache.has(filename)) {
    return cache.get(filename)
  } else {
    const data = readFileSync(filename, 'utf8')
    cache.set(filename, data)
    return data
} }
console.log(consistentReadSync("data.txt"))
// the next call will read from the cache
console.log(consistentReadSync("data.txt"))

We can see that the entire function was also converted into a direct style. There’s no reason for a function to have a CPS if it’s synchronous. In fact, it’s always best practice to implement a synchronous API using a direct style. This will eliminate any confusion around its nature and will also be more efficient from a performance perspective.

Pattern

Always choose a direct style for purely synchronous functions.

Remember that changing an API from CPS to a direct style, or from asynchronous to synchronous or vice versa, might also require a ...