Mastering Delayed Execution in JavaScript: Waiting 5 Seconds Between Lines

Pausing execution between JavaScript lines or statements is a common need when building complex applications, UI flows, animations, APIs, and more. Whether you need to allow time for asynchronous logic to complete, prevent overloading APIs, deliberately throttle performance, or simply build smoother UX transitions – having control over execution timing is critical.

In this comprehensive guide, you’ll learn expert techniques to wait, delay, or pause 5 full seconds before executing the next line of JavaScript code.

Why You Need Control Over Delayed Execution

Let me provide some specific examples that illustrate the importance of controlling execution delays in JavaScript:

Smoother UI/UX Animations

Imagine you want to slowly display an animated progress bar indicating loading time. By deliberately waiting/pausing 100 milliseconds between each progress update, you can create a clean animated transition:

function loadProgress() {

  showProgressBar();  

  wait(100);
  updateProgress(25);

  wait(100);
  updateProgress(50);

  // ...
}

Having fine-grained control over the timing here allows us to dictate an optimal visualization pace.

Prevent Overloading APIs

If you are making rapid calls to external APIs in a loop, pausing 2 to 3 seconds between each call can prevent hitting rate limits or overloading APIs:

async function submitData(data) {

  for(let i = 0; i < requests.length; i++) {

    await externalAPI.submit(requests[i]);

    // Prevent flooding API
    await sleep(3000); 
  }

}

The pauses throttle throughput to avoid failures.

Allow Async Logic to Finish

You may also need to wait up to N seconds before executing a line of code to allow time for other asynchronous operations to finish in the background:

startSpinner();

// Allow up to 10s for fetch  
await raceToComplete(
  fetchAsyncData(), 
  wait(10000)  
);

stopSpinner();

Here we ensure the spinner displays for at least 10 seconds to prevent jarring transitions.

These examples demonstrate just some of the key cases. Now let’s explore expert techniques that enable precise delayed execution.

Two Primary Methods for Delaying Execution

In JavaScript, there are two common approaches to delay execution for a specified time:

1. setTimeout() – Schedule code to execute after an elapsed timeframe
2. Custom sleep() – Leverage promises and async/await for sequential syntax

The techniques have slightly different use cases which I’ll cover in-depth.

setTimeout(): Simple Delayed Execution

The setTimeout() function is used to schedule execution of a callback function after a minimum elapsed time (defined in milliseconds):

setTimeout(callback, 2500); // Wait 2.5 seconds

This will pause for a minimum of 2.5 seconds before executing the callback handling logic.

Here is a full example:

console.log("App Start");

function delayedLog() {
   console.log("Executing callback!")  
}

setTimeout(delayedLog, 5000); // Wait 5 seconds

console.log("App End"); 

Output:

App Start 
App End
Executing callback!

After 5 seconds the delayedLog() callback executes.

The setTimeout() function is quite simple to use for basic cases needing a single delayed execution. However, for sequential scenarios it can become more complex.

Now let‘s look at how we can leverage promises and async/await to make this easier.

Custom sleep() with async/await

For more flexibility, we can create a custom sleep() function and leverage the async/await syntax:

function sleep(ms) {
  return new Promise(resolve => setTimeout(resolve, ms));
}

async function delayedLog() {

  console.log("Start");

  await sleep(5000); // Wait 5 seconds

  console.log("Done!");  
}

By using JavaScript promises and async/await, we gain a few advantages:

• Custom reusable sleep() function abstracts away delay logic
• Code reads synchronously while executing asynchronously
• Error handling with try/catch blocks
• More flexibility composing sequenced delays

For example, we can pause multiple times easily:

async function sequence() {

  console.log("Start");

  await sleep(2000); 
  // Do some work

  await sleep(5000);
  // Do more work    

  console.log("End");

}

sequence(); 

This allows us to dictate a full sequence with precise delays in a simple procedural style.

So while setTimeout() is great for one-off delays, async/await helps orchestrate complex sequenced pauses in execution.

Diving Deeper into Async/Await Syntax

Since async/await is such a useful syntax for delayed execution, let‘s do a deeper dive into how it works with promises under the covers.

Remember, async functions always return a promise:

async function myFunc() {
  return "Hello"; 
}

const promise = myFunc(); // Promise that resolves to "Hello"

Within the async function body, we use await on promise-based function calls to effectively "pause" execution until that promise settles.

For example:

function wait(ms) {
  return new Promise(resolve => {   
    setTimeout(resolve, ms);
  });
}

async function hello() {

  await wait(5000); // Pause 5s for promise 

  return "World!";

}

hello().then(msg => {
  console.log(msg); // "World!" (after 5s delay)  
});

So await allows us to write synchronous style code within the async function while not actually blocking execution. The event loop continues processing other logic while paused.

This makes async/await a very clean syntax for delayed execution cases compared to traditional promise chaining.

Which Delay Approach Should You Use?

So when should you use setTimeout() vs a custom sleep() function with async/await to delay JavaScript execution?

Here is a helpful comparison:

Approach	Use Cases
setTimeout()	Basic single delay requirements Fast background threading Simple chron jobs
async sleep()	Sequenced pauses Waterfalls/cascades UIs/animations Throttling

setTimeout() tends to be best for relatively basic cases that don‘t need sequential coordination. The timers execute very efficiently.

async sleep() shines when coordinating cascading asynchronous actions in order. Working with promises does have a bit more overhead, so avoid unnecessary pauses.

Statistics on Delay Impact

When delaying execution, we need to be aware of potential downsides like increased memory usage and blocking:

As shown in the statistics, short delays under 100ms have very little impact, while 500ms+ pauses can start blocking the event loop more substantially.

So while delays are extremely useful, keep memory usage and blocking in mind, especially for long durations. By following best practices, you can minimize negative side effects.

Concurrency Patterns

In performance sensitive applications, we want logic to execute concurrently whenever possible while using delays.

Let‘s look at some examples of running operations concurrently with delays.

Parallel Execution with Timers

Using setTimeout() we can trigger multiple branches to execute separately after different delays:

setTimeout(() => {
  // Branch A     
}, 2500); 

setTimeout(() => {
  // Branch B
}, 5000);

After 2.5 seconds branch A starts while branch B doesn‘t start for 5 full seconds. They run independently so the total execution time is just over 5 seconds.

Promise.all()

If you need synchronization after a set of async operations complete, Promise.all() is perfect:

async function main() {

  const fetchA = fetchResource("A");
  const fetchB = fetchResource("B");

  await Promise.all([fetchA, fetchB]);

  // Continues after both fetches complete  
}

main();

This allows both resource fetches to run concurrently, reducing total time.

Promise.all is enormously useful for synchronized concurrency with async/await flows.

Abort Controllers

We can also use AbortController to cancel async operations programmatically after a certain timeout:

const controller = new AbortController();
const signal = controller.signal;

setTimeout(() => controller.abort(), 5000);

try {

  await fetchResource({ signal });
  // Fetch continues for up to 5 seconds

} catch (e) {

  // Handle abort  
}

After 5 seconds, we automatically abort the fetch. Useful for controlling worst case waits.

So there are certainly a variety of patterns at our disposal to run operations concurrently while still incorporating precise delays.

Debugging WITH Delays

One excellent use case for delayed execution is debugging.

Strategically waiting between lines gives us increased visibility into intermediate state during execution.

Here is an example using setTimeout():

function processOrder(order) {

  console.log(`Received order: `, order);

  // Log state after 5s 
  setTimeout(() => {
    console.log(`State after 5s:`, state);
  }, 5000);

  // Complex logic...   

  fulfillOrder(order);

}

By checking state mid-way through the function, we can validate that the right data transforms occurred early in execution before errors occur later.

In async functions, we can also immediately pause execution on the first line by adding a delay early on:

async function syncData() {

  await sleep(9000); // Check initial state & inputs

  // Remainder of function

}

This allows us time to check calls, inputs, database connections, etc. before reaching more complex logic.

So while delays impact performance in production code, they become invaluable during debugging by granting visibility into intermediate state.

Key Takeaways & Best Practices

Here are some top take-aways to apply in your projects:

• Prefer setTimeout() for basic delays & async/await for sequenced logic flows
• Minimize blocking the event loop with long delays when possible
• Use delays to strategically throttle throughput to prevent flooding
• Design asynchronous & non-blocking architecture, then orchestrate with delays
• Document your delays to help future maintainers understand intent
• Always handle promise rejections correctly inside async functions

By thoughtfully using delayed execution, you can craft robust applications, achieve high performance under load, and build slick UIs with smooth visual transitions.

Conclusion & Next Steps

Whether you need to throttle APIs, prevent resource exhaustion, enable complex UI animations, or simply pause before the next JavaScript statement – having control over execution timing is critical.

With a combination of setTimeout() and async/await techniques, we can build resilient applications that incorporate the exact delays we need for stability and percise execution sequencing.

For next steps, consider researching additional patterns like requestAnimationFrame() that further optimize animated transitions to achieve 60 FPS rendering. Fine-tuning execution timing unlocks higher quality UX.

I hope this guide gives all full-stack and front-end experts the knowledge needed to perfectly craft delayed execution sequences. Feel free to reach out with any other questions!