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  3. Prepend Characters or Words to a String in JavaScript or Node.js

Prepend Characters or Words to a String in JavaScript or Node.js

Working with string values comes with some typical problems. One of them is to add a prefix to an existing string. For example, you might compose a URL and want a given URL path with a leading forward slash in case it’s not present on the current value.

This tutorial shows you how to add a prefix to the head of a string in JavaScript.

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Add a String to the Beginning of Another String in JavaScript

JavaScript comes with built-in operators. One of them is the + operator. You can prepend a string to an existing string value using the + operator:

const studio = ' Studio'  
const appended = 'Future' + studio  
// 'Future Studio'

Please notice: when using the + operator with the first argument being a string, JavaScript casts the second parameter to a string as well. In case the second argument is undefined or null you’ll end up adding the 'undefined' or 'null' strings to the first one:

const studio = ' Studio'

const appendedUndefined = undefined + studio  
// 'Future undefined'

const appendedNull = null + studio  
// 'Future null'

You can also add a prefix to a string using template strings. Template literals . You’re writing your string as always and add the values from variables using the ${<variable>} syntax:

const future = 'Future'

const prepended = `${future} Studio`  
// 'Future Studio'

const appendedUndefined = `${undefined} Studio`  
// 'undefined Studio'

const appendedNull = `${null} Studio`  
// 'null Studio'

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#prepend method.

The prepend method prefixes a given text to the beginning of a string. It won’t prepend undefined or null values and instead leaves the source string “as is”. This package allows you to further chain methods for more customizations:

import { Str } from '@supercharge/string'

Str('Studio').prepend().get()  
// 'Studio'

Str('Studio').prepend(null).get()  
// 'Studio'

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

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

Enjoy prefixing strings!

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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