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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.
Deferring a Simple Function:
4.2.
JavaScript
4.3.
Updating UI After Initial Load:
4.4.
JavaScript
4.5.
Deferring Function with Multiple Arguments:
4.6.
JavaScript
4.7.
Using Defer in Event Handlers:
4.8.
JavaScript
5.
Frequently Asked Questions 
5.1.
How does _.defer() differ from setTimeout(func, 0)?
5.2.
Can the deferred function be cancelled?
5.3.
Is _.defer() suitable for heavy computational tasks?
6.
Conclusion
Last Updated: Mar 27, 2024
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Lodash _.defer() Method

Author Rinki Deka
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Introduction

Managing the execution timing of functions is a common need in JavaScript, especially when deferring actions until the current call stack has cleared. Lodash provides the _.defer() method for this purpose. This function delays the invocation of a function until the current call stack has cleared, akin to using setTimeout with a delay of 0. 

Lodash _.defer() Method

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

Why This Function is Used

The _.defer() function is used to delay the execution of a function until the current call stack is complete. This is particularly useful in scenarios where you want to ensure that the rest of your code executes before a specific function, or when attempting to execute a function outside the current execution phase, such as updating the UI or handling resource-intensive calculations after initial loading.

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Syntax, Parameter and Return Value

Syntax: 

_.defer(func, [...args])

Parameters:

  • func (Function): The function to defer.
     
  • [...args]: The arguments to invoke the function with.

Return Value: 

(number) - Returns the timer ID for cancelling the deferred function (similar to setTimeout).

Examples 

Deferring a Simple Function:

  • JavaScript

JavaScript

var _ = require('lodash');

function greet(name) {

 console.log('Hello, ' + name);

}

_.defer(greet, 'John');

Output (after the current call stack clears): 

'Hello, John'


Demonstrates deferring a simple greeting function.

Updating UI After Initial Load:

  • JavaScript

JavaScript

function updateUI() {

 console.log('UI updated');

}

_.defer(updateUI);


// UI update code will execute after the current call stack, such as initial page load, is complete.

Shows deferring a UI update function until after the page has loaded.

Deferring Function with Multiple Arguments:

  • JavaScript

JavaScript

function logDetails(a, b, c) {

 console.log(a, b, c);

}

_.defer(logDetails, 'apple', 'banana', 'cherry');

Output:

'apple banana cherry' (deferred execution)


An example of deferring a function that takes multiple arguments.

Using Defer in Event Handlers:

  • JavaScript

JavaScript

document.getElementById('myButton').addEventListener('click', () => {

 _.defer(() => console.log('Button clicked'));

});

// The message 'Button clicked' will be logged after the click event handling is complete.

Demonstrates using _.defer() within an event handler for post-processing.

Frequently Asked Questions 

How does _.defer() differ from setTimeout(func, 0)?

_.defer() is similar to setTimeout(func, 0) but is more concise and readable. It's specifically designed for deferring function execution, making code intentions clearer.

Can the deferred function be cancelled?

Yes, the returned timer ID from _.defer() can be used with clearTimeout to cancel the deferred function before it executes.

Is _.defer() suitable for heavy computational tasks?

While _.defer() is useful for delaying tasks, heavy computations might still block the UI thread. For such tasks, Web Workers or breaking the task into smaller chunks may be more appropriate.

Conclusion

Lodash's _.defer() method provides a simple and effective way to postpone function execution until after the current call stack is cleared. It's particularly useful for deferring tasks that need to run after the immediate execution flow, such as UI updates or post-processing operations.

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