Creating a Command Line Interface (CLI) application in JavaScript for the browser: A guide to simulating blocking I/O

Question

Creating a Command Line Interface (CLI) application in JavaScript for the browser: A guide to simulating blocking I/O

Developing a CLI application becomes quite simple with a blocking I/O API like PrintLn / ReadLn, making the process smooth and efficient.

However, the challenge arises when trying to create a terminal application that runs on a browser using JS. In this scenario, input events are asynchronous, which means you cannot block the function midway through while waiting for input without disrupting the application's state.

I am currently grappling with designing the event loop and structuring the architecture of the JavaScript code. This is especially tricky as there will be multiple levels of commands within the app, and I want to avoid falling into the trap of "callback hell". Could someone please guide me to a resource or provide tips on how to architect this design? Thank you.

javascript

Answer 1

Answer №1

Implementing Promises in Your Code

Submit user input
Disable new input submission temporarily
Invoke a Promise function
Show the result after the Promise has been fulfilled
Enable terminal for new inputs

// Triggering the operation upon submitting
function submit(userInput) => {

  // Temporarily disable terminal
  blockTerminal();

  // Processing the user's command
  // Invoking an async Promise
  // Result displayed once operation is complete
  doSomething(userInput).then(result => {

    // Displaying outcome in the terminal
    output(result);

    // Re-enable terminal for new inputs
    releaseTerminal();
  })
}

// The asynchronous code being executed
// Returns a Promise object
function doSomething(userInput) => {
  return new Promise(resolve => {

    // Simulating a delay of 2500ms
    setTimeout(() => {
      resolve('result')
    }, 2500)
  })
}

In a live environment, replace setTimeout() with an Ajax call and use resolve(response) upon success.

Alternatively, consider exploring RxJS.

RxJS introduces Observable streams in JavaScript, which are highly effective for handling asynchronous operations. Though more complex than Promises, they offer powerful functionalities.

Answer 2

Implementing Promises in Your Code

Submit user input
Disable new input submission temporarily
Invoke a Promise function
Show the result after the Promise has been fulfilled
Enable terminal for new inputs

// Triggering the operation upon submitting
function submit(userInput) => {

  // Temporarily disable terminal
  blockTerminal();

  // Processing the user's command
  // Invoking an async Promise
  // Result displayed once operation is complete
  doSomething(userInput).then(result => {

    // Displaying outcome in the terminal
    output(result);

    // Re-enable terminal for new inputs
    releaseTerminal();
  })
}

// The asynchronous code being executed
// Returns a Promise object
function doSomething(userInput) => {
  return new Promise(resolve => {

    // Simulating a delay of 2500ms
    setTimeout(() => {
      resolve('result')
    }, 2500)
  })
}

In a live environment, replace setTimeout() with an Ajax call and use resolve(response) upon success.

Alternatively, consider exploring RxJS.

RxJS introduces Observable streams in JavaScript, which are highly effective for handling asynchronous operations. Though more complex than Promises, they offer powerful functionalities.

Answer 3

Answer №2

To accomplish this, you can utilize the async/await functionality.

function fetchInput(){
  return new Promise(response =>{
    document.querySelector('#submit').addEventListener('click', () => response(document.querySelector('#inputValue').value, {once:true}))
  })
}

async function execute(){
  for(let i=0;;++i){
    let input = await fetchInput()
    console.log(`${i}:${input}`)
  }
}

execute()

<input type="text" id="inputValue">
<input type="button" value="Submit" id="submit">

Answer 4

To accomplish this, you can utilize the async/await functionality.

function fetchInput(){
  return new Promise(response =>{
    document.querySelector('#submit').addEventListener('click', () => response(document.querySelector('#inputValue').value, {once:true}))
  })
}

async function execute(){
  for(let i=0;;++i){
    let input = await fetchInput()
    console.log(`${i}:${input}`)
  }
}

execute()

<input type="text" id="inputValue">
<input type="button" value="Submit" id="submit">

Creating a Command Line Interface (CLI) application in JavaScript for the browser: A guide to simulating blocking I/O

Answer №1

Answer №2

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