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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.
Creating a Specific Logger Function:
4.2.
JavaScript
4.3.
Pre-filling Arguments for Event Handlers:
4.4.
JavaScript
4.5.
Setting Default Parameters for API Calls:
4.6.
JavaScript
4.7.
Creating a Bind Function for Specific Element:
4.8.
JavaScript
5.
Frequently Asked Questions 
5.1.
Can _.partial() handle functions with multiple arguments?
5.2.
How does _.partial() differ from _.bind()?
5.3.
Is it possible to use _.partial() with asynchronous functions?
6.
Conclusion
Last Updated: Mar 27, 2024
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Lodash _.partial() Method

Author Rahul Singh
0 upvote
Roadmap to SDE career at Amazon
Speaker
Anubhav Sinha
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25 Jun, 2024 @ 01:30 PM

Introduction

Function customization through pre-setting some of its arguments can significantly enhance flexibility and reusability in programming. Lodash caters to this need with the _.partial() method. This function creates a new function with partially applied arguments, meaning that it pre-fills some of a function's arguments and returns a new function ready to take the remaining ones. This technique, known as partial application, is particularly useful for creating more specific functions from general ones. 

Lodash _.partial() Method

This article will explore the _.partial() method, its syntax, applications, and advantages, supported by examples and FAQs.

Why This Function is Used

The _.partial() function is used to create new functions by fixing a certain number of arguments of an existing function. It's particularly useful in scenarios where you need to frequently call a function with mostly the same arguments, but still want to maintain some level of flexibility. By partially applying arguments, _.partial() allows for the creation of function variants that are more specific yet maintain the core functionality of the original function.

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Syntax, Parameter and Return Value

Syntax: 

_.partial(func, [partials])

Parameters:

  • func (Function): The function to partially apply arguments to.
     
  • [partials]: The arguments to be partially applied.

Return Value: 

(Function) - Returns the new partially applied function.

Examples 

Creating a Specific Logger Function:

  • JavaScript

JavaScript

var _ = require('lodash');

function logger(level, message) {

 console.log(`[${level}] - ${message}`);

}

var infoLogger = _.partial(logger, 'INFO');

infoLogger('System is up and running'); 



Output

'[INFO] - System is up and running'


Demonstrates creating a specific logger function for the 'INFO' level.

Pre-filling Arguments for Event Handlers:

  • JavaScript

JavaScript

function handleEvent(eventName, event) {

 console.log(`Event ${eventName} occurred:`, event.type);

}

var handleMouseClick = _.partial(handleEvent, 'Mouse Click');

document.addEventListener('click', handleMouseClick);


// On click, logs: 'Event Mouse Click occurred: click'

Shows using _.partial() to create a specific event handler for mouse clicks.

Setting Default Parameters for API Calls:

  • JavaScript

JavaScript

function fetchData(url, queryParams) {

 console.log(`Fetching data from ${url} with params`, queryParams);

 // API call logic

}

var fetchUser = _.partial(fetchData, '/api/users', { active: true });

fetchUser();


// Fetching data from /api/users with params { active: true }

An example of using _.partial() to set default parameters for an API call function.

Creating a Bind Function for Specific Element:

  • JavaScript

JavaScript

function bindToElement(element, data) {

 element.textContent = JSON.stringify(data);

}

var bindToMyElement = _.partial(bindToElement, document.getElementById('myElement'));

bindToMyElement({ key: 'value' });


 // Binds { key: 'value' } to the 'myElement' element

Demonstrates creating a function to bind data to a specific DOM element.

Frequently Asked Questions 

Can _.partial() handle functions with multiple arguments?

Yes, _.partial() can be used with functions that take multiple arguments. It allows you to pre-fill any number of these arguments as needed.

How does _.partial() differ from _.bind()?

While both _.partial() and _.bind() can pre-fill arguments, _.bind() also sets the this context of the function, whereas _.partial() only deals with arguments.

Is it possible to use _.partial() with asynchronous functions?

Yes, _.partial() can be used with asynchronous functions, including functions that return promises. It works by pre-filling arguments, regardless of the function's synchronous or asynchronous nature.

Conclusion

Lodash's _.partial() method is a powerful tool for creating more specific functions from general ones by pre-filling some of their arguments. It enhances the flexibility and modularity of function calls, allowing for more concise and targeted function execution.

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