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  3. Ensure a String Ends with a Given Character in JavaScript or Node.js

Ensure a String Ends with a Given Character in JavaScript or Node.js

In some situations, it’s useful to ensure an ending character on a string value. For example, you always want route paths in your web application to end with a trailing slash. Or you want to ensure a base URL for API requests already has a trailing slash before appending path or query parameters.

This tutorial shows how to ensure a string value ends with a given character.

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Make Sure a String Ends With a Character Using JavaScript

We’re building web applications that interact with other platforms. For example, we’re requesting data from GitHub by making API requests to different endpoints. Composing the API endpoint URL uses the base URL of GitHub’s API and we’re usually adding a trailing slash to that stored base URL.

Here’s an exemplary API client storing the base URL in a variable:

let baseUrl = 'https://futurestud.io/tutorials'

if (!baseUrl.endsWith('/')) {  
  baseUrl = `${baseUrl}/`
}

If the baseUrl already ends a slash you're leaving it "as is“.

From there the base URL has a trailing slash. Combining it with endpoint URLs may lead in a double-slash situation when the endpoint path starts with a leading slash:

const endpointUrl = `${baseUrl}/some-endpoint-url`  
// baseUrl-with-trailing-slash//some-endpoint-url

Please check out the tutorials here on Future Studio on how to front-trim characters off a string or how to end-trim characters off a string to resolve this situation.

Use the @supercharge/strings Package

I’m the maintainer of the @supercharge/strings package providing convenient string utilities. The @supercharge/strings package comes with a handy Str#finish(character) method.

This finish method ensures that the string ends with a given character:

import { Str } from '@supercharge/string'

Str('https://futuresstud.io/tutorials').finish('/').get()  
// https://futuresstud.io/tutorials/

Str('https://futuresstud.io/tutorials////').finish('/').get()  
// https://futuresstud.io/tutorials////

The second example with uses a base string that already has the desired character at the end. In such cases you may want to trim existing characters from the end of the string before ensuring that the string ends with it.

The @supercharge/strings package comes with rtrim(characters? method removing whitespaces from the end of a given string or the provided characters:

import { Str } from '@supercharge/string'

Str('https://futuresstud.io/tutorials////').rtrim('/').finish('/').get()  
// 'https://futuresstud.io/tutorials/'

Enjoy making sure strings end with a character!

Mentioned Resources

Marcus Pöhls

Marcus is a fullstack JS developer. He’s passionate about the hapi framework for Node.js and loves to build web apps and APIs. Creator of Futureflix and the “learn hapi” learning path.

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