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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.
Checking for a Specific Prefix in a String:
4.2.
JavaScript
4.3.
Validating URL Protocols:
4.4.
JavaScript
4.5.
Searching from a Specific Position:
4.6.
JavaScript
4.7.
Filtering Data Based on Prefix:
4.8.
JavaScript
5.
Frequently Asked Questions
5.1.
How does _.startsWith() differ from using String.prototype.startsWith()?
5.2.
Can _.startsWith() handle case-sensitive checks?
5.3.
Is _.startsWith() suitable for checking multiple possible starts?
6.
Conclusion
Last Updated: Mar 27, 2024
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Lodash _.startsWith() Method

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Introduction

In string manipulation and validation tasks, checking if a string begins with a specific substring is a common operation. Lodash's _.startsWith() method offers a concise and straightforward way to perform this check.

Lodash _.startsWith() Method

It's especially useful in scenarios such as validating input formats, filtering data based on prefixes, or implementing custom search functionalities.

Why This Function is Used

The _.startsWith() function is used to determine if a string starts with a given target substring. This is essential in situations where the beginning of a string signifies specific information, such as file extensions, protocol types in URLs, or categorization prefixes in data entries.

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Syntax, Parameter and Return Value

Syntax:

 _.startsWith([string=''], [target], [position=0])

Parameters:

  • [string=''] (string): The string to inspect.
     
  • [target] (string): The string to search for.
     
  • [position=0] (number): The position to start the search at.

Return Value: 

(boolean) - Returns true if string starts with target, else false.

Examples 

Checking for a Specific Prefix in a String:

  • JavaScript

JavaScript

var _ = require('lodash');

var text = 'hello world';

console.log(_.startsWith(text, 'hello'));

Output: 

true


Demonstrates checking if a string starts with a specific word.

Validating URL Protocols:

  • JavaScript

JavaScript

var url = 'https://www.example.com';

console.log(_.startsWith(url, 'https'));

Output:

 true


Shows how to validate the protocol of a URL.

Searching from a Specific Position:

  • JavaScript

JavaScript

var sentence = 'This is a test';

console.log(_.startsWith(sentence, 'is', 2));

Output: 

true


An example of using the position parameter to check for a substring starting at a specific index in the string.

Filtering Data Based on Prefix:

  • JavaScript

JavaScript

var filenames = ['report.txt', 'image.jpg', 'script.js'];

var txtFiles = filenames.filter(name => _.startsWith(name, 'report'));

console.log(txtFiles);

Output:

 ['report.txt']


Demonstrates filtering an array of strings based on a prefix.

Frequently Asked Questions

How does _.startsWith() differ from using String.prototype.startsWith()?

_.startsWith() is Lodash's implementation and is similar to JavaScript's native startsWith() method. The primary difference is that Lodash methods like _.startsWith() can be chained with other Lodash utilities for more complex operations.

Can _.startsWith() handle case-sensitive checks?

_.startsWith() is case-sensitive. For case-insensitive checks, you should convert both the string and target to the same case (e.g., using .toLowerCase()).

Is _.startsWith() suitable for checking multiple possible starts?

For multiple starts, _.startsWith() would need to be used in conjunction with other methods, like Array.prototype.some(), to check each potential start string.

Conclusion

Lodash's _.startsWith() method is an effective tool for verifying whether a string begins with a specified substring. It's particularly useful for string validation, searching, and filtering tasks where the start of the string is significant.

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