2. Tutorials
  3. JavaScript — Cache Computation Results in a Local Variable

JavaScript — Cache Computation Results in a Local Variable

We’re using a small performance optimization in our code bases: caching computation results in local variables. Saving results in a local variable is borrowed from the memoization technique. Memoizing values improves the performance of function execution by storing the results and reusing them for a function call.

This tutorial shows you how to use local caching of computation results to increase your code’s processing performance.

Node.js Series Overview

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  24. How to Count Words in a File
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  26. Append Characters or Words to a String in JavaScript or Node.js
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  31. Lowercase the First Character of a String in JavaScript or Node.js
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  33. Prepend Characters or Words to a String in JavaScript or Node.js
  34. Check if a String is a Number
  35. Convert a String to Buffer
  36. Prevent Line Breaks in String Template Literals
  37. How to Implement a Custom `toString` Method (Coming soon)
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Use In-Memory Caching for Faster Code Processing

Imagine an Application class that provides details of your project. For example, you’re accessing the application’s name through this Application class. The application name comes from the name property of the package.json file. Here’s the optimization idea: you’re reading and parsing the contents of the package.json file once and keep it memorized in a local property.

Here’s the sample code of the application class that reads and stores the contents of the project’s package.json file:

import Fs from 'node:fs'  
import Path from 'node:path'

export class Application {  
  /**
   * Create a new application instance.
   */
  constructor () {
    this.meta = {
      packageJson: undefined,
    }
  }

  /**
   * Returns the app name.
   */
  name () {
    return this.packageJson().name
  }

  /**
   * Returns the object of the application’s `package.json` file.
   */
  private packageJson () {
    if (this.meta.packageJson != null) {
      return this.meta.packageJson
    }

    const packageJsonPath = Path.resolve(__dirname, 'package.json')

    if (!Fs.existsSync(packageJsonPath)) {
      throw new Error(`Cannot find "package.json" in application base path: "${packageJsonPath}"`)
    }

    this.meta.packageJson = JSON.parse(
      Fs.readFileSync(packageJsonPath).toString()
    )

    return this.meta.packageJson
  }
}

Here’s how you could use the Application class and its memoized values:

const app = new Application()

console.log(app.name())  
// reads the `package.json` file from disk and returns the "name" property from it

console.log(app.name())  
// uses the in-memory `package.json` content and returns the "name" property from it

You can use in-memory caching to store all kinds of computations. Typically, you’re storing resource-intensive results to avoid redundant processing. A good candidate for local caching is the result of reading and parsing a file from local hard disk, because the file may not change until restarting the Node.js process.

That’s it!

Marcus Pöhls

Marcus is a fullstack JS developer. He’s passionate about the hapi framework for Node.js and loves to build web apps and APIs. Creator of Futureflix and the “learn hapi” learning path.

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