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Table of contents
1.
Introduction
2.
Why This Function is Used
3.
Syntax, Parameter and Return Value
3.1.
Syntax: 
3.2.
Parameters:
3.3.
Return Value: 
4.
Examples 
4.1.
Executing After Multiple Events:
4.2.
JavaScript
4.3.
Handling Multiple Async Operations:
4.4.
JavaScript
4.5.
Loading Multiple Resources:
4.6.
JavaScript
4.7.
Batch Processing Completion:
4.8.
JavaScript
5.
Frequently Asked Questions 
5.1.
What happens if _.after() is called with n less than or equal to 1?
5.2.
Can _.after() be reset or does it persist its count state?
5.3.
Is _.after() suitable for managing event handlers?
6.
Conclusion
Last Updated: Mar 27, 2024
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Lodash _.after() Method

Author Rinki Deka
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Anubhav Sinha
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12 Jun, 2024 @ 01:30 PM

Introduction

In JavaScript programming, controlling the execution of functions based on a certain number of calls can be crucial, especially in scenarios involving repetitive or callback-based operations. The Lodash library offers a helpful function, _.after(), designed for this purpose. This function creates a version of the given function that only executes after being called a specified number of times. 

Lodash _.after() Method

This article will explore the _.after() method, detailing its syntax, use cases, and advantages, illustrated through examples and FAQs.

Why This Function is Used

The _.after() function is used to ensure that a particular function is executed only after it has been called a specific number of times. This is particularly useful in situations like handling repetitive events, ensuring that a callback is executed only after a certain number of operations have completed, or managing the order of function executions in asynchronous processes. It provides a straightforward mechanism for controlling function execution flow based on call count.

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Syntax, Parameter and Return Value

Syntax: 

_.after(n, func)

Parameters:

  • n (number): The number of calls before func is executed.
     
  • func (Function): The function to restrict.

Return Value: 

(Function) - Returns the new restricted function.

Examples 

Executing After Multiple Events:

  • JavaScript

JavaScript

var _ = require('lodash');

var save = () => console.log('Saving data...');

var saveAfterThreeCalls = _.after(3, save);

saveAfterThreeCalls(); // Not yet called 3 times.

saveAfterThreeCalls(); // Not yet called 3 times.

saveAfterThreeCalls();

Output: 

'Saving data...'


Demonstrates delaying function execution until it's been called three times.

Handling Multiple Async Operations:

  • JavaScript

JavaScript

var completeOperation = _.after(2, () => console.log('Operations completed.'));

// Simulating asynchronous operations

setTimeout(completeOperation, 100); // First async operation completed.

setTimeout(completeOperation, 200);

Output: 

'Operations completed.'


Shows executing a function after completing multiple asynchronous operations.

Loading Multiple Resources:

  • JavaScript

JavaScript

var resourcesLoaded = _.after(5, () => console.log('All resources loaded.'));

// Assuming each 'loadResource' invocation is triggered after a resource is loaded.

for (let i = 0; i < 5; i++) {

 loadResource(resourcesLoaded);

}

Output after 5th resource:

 'All resources loaded.'


An example of using _.after() to execute a callback after loading multiple resources.

Batch Processing Completion:

  • JavaScript

JavaScript

var processBatch = _.after(10, () => console.log('Batch processing complete.'));

for (let i = 0; i < 10; i++) {

 processItem(i, processBatch);

}

 Output after 10th item:

 'Batch processing complete.'


Demonstrates using _.after() to notify when batch processing is complete.

Frequently Asked Questions 

What happens if _.after() is called with n less than or equal to 1?

If n is less than or equal to 1, the function func will execute immediately upon its first call.

Can _.after() be reset or does it persist its count state?

The count state in _.after() persists; it doesn't reset. Once the function has been executed, subsequent calls will always execute the function.

Is _.after() suitable for managing event handlers?

Yes, _.after() can be effective for managing event handlers, especially when an action should only be triggered after an event has occurred a specific number of times.

Conclusion

Lodash's _.after() method is a practical tool for controlling the execution of functions based on the number of times they are called. It is particularly useful in managing sequential operations, batch processes, and coordinating actions in asynchronous workflows.

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