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  3. Left-Trim Characters Off a String in JavaScript or Node.js

Left-Trim Characters Off a String in JavaScript or Node.js

When working with strings you may want to trim off characters from the start of the value. For example, when composing a request URL you may combine a base URL with an endpoint URL. You want to make sure you’re not ending the base URL with a trailing and starting the endpoint URL with a leading slash.

This tutorial shows you how to remove whitespaces or characters from the beginning of a string value.

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Trim Characters From the Start of a String Using JavaScript

This tutorial uses URLs as references for the string trimming. You may need to remove characters from the beginning of a string in another situation. Please map this use-case to your own needs.

One use-case to concatenate strings is the composition of a final request URL. You append an endpoint URL path to a base URL and want to avoid a double-slash situation this like:

const baseUrl = 'https://api.github.com/'  
const repositoryEndpointUrl = '/users/futurestudio/repos'

const requestUrl = baseUrl + repositoryEndpointUrl  
// ⚡️  https://api.github.com//users/futurestudio/repos
//     -> see the double slash after ".com"

Intuitively you may remove the slash from the base URL or the endpoint URL. But you can’t ensure everyone is using the URLs the same way as you expect to. A solution is to implement some string handling that ensures you’re always removing a leading slash from the endpoint URLs and keep the trailing slash on the base URL.

Here’s a sample function removing whitespaces or provided characters from the start of a string:

/**
 * Removes whitespaces from the head of the string when
 * no argument value is present. It trims the provided `character`
 * from the left of the string if you pass along a value.
 *
 * @param {String} character
 *
 * @returns {Boolean}
 */
function ltrim (string, character) {  
  character = character || ''

  if (!character) {
    return string.trimStart()
  }

  while (string.startsWith(character)) {
    string = string.slice(character.length)
  }

  return string
}

You can use the ltrimutility method like this:

ltrim('  Future Studio')  
// 'Future Studio'

ltrim('  Future Studio  ')  
// 'Future Studio  '

ltrim('/url-path', '/')  
// 'url-path'

ltrim('///url-path', '/')  
// 'url-path'

ltrim('some-value-not-starting-with-the-replacer', '/')  
// 'some-value-not-starting-with-the-replacer'

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#ltrim(characters?) method.

This ltrim method removes whitespaces from the end of a given string or the provided characters:

import { Str } from '@supercharge/string'

Str('  Future Studio').ltrim().get()  
// 'Future Studio'

Str('  Future Studio  ').ltrim().get()  
// 'Future Studio  '

Str('/url-path').ltrim('/').get()  
// 'url-path'

Str('///url-path').ltrim('/').get()  
// 'url-path'

Str('some-value-not-starting-with-the-replacer').ltrim('/').get()  
// 'some-value-not-starting-with-the-replacer'

Enjoy removing characters from the head of a string!

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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