String.raw in Tailwind CSS source code.

In this article, we analyze the usage of String.raw in Tailwindcss source code.

String.raw

MDN documentation says that:

“The String.raw() static method is a tag function of template literals.

This is similar to the r prefix in Python, or the @ prefix in C# for string literals.

It’s used to get the raw string form of template literals — that is, substitutions

(e.g. ${foo}) are processed, but escape sequences (e.g. \n) are not.“

Example 1:

The below example is picked from MDN:

// Create a variable that uses a Windows
// path without escaping the backslashes:
const filePath = String.raw`C:\Development\profile\aboutme.html`;
console.log(`The file was uploaded from: ${filePath}`);
// Expected output: "The file was uploaded from: C:\Development\profile\aboutme.html"

This above example’s execution result looks like this:

> "The file was uploaded from: C:\Development\profile\aboutme.html"

Example 2:

If you run the same example without String.raw using the code below:

// Create a variable that uses a Windows
// path without escaping the backslashes:
const filePath = `C:\Development\profile\aboutme.html`;
console.log(`The file was uploaded from: ${filePath}`);
// Expected output: "The file was uploaded from: C:\Development\profile\aboutme.html"

Result looks like this:

> "The file was uploaded from: C:Developmentprofileaboutme.html"

Example 3:

If you run the same example involving \n using the code below:

const filePathWithoutStringRaw = `\nC:\Development\profile\aboutme.html`;
const filePathWithStringRaw = String.raw`\nC:\Development\profile\aboutme.html`;
console.log("filePathWithoutStringRaw:", filePathWithoutStringRaw)
console.log("*******")
console.log("filePathWithStringRaw:", filePathWithStringRaw)

Result looks like this:

> "filePathWithoutStringRaw:" "
C:Developmentprofileaboutme.html"
> "*******"
> "filePathWithStringRaw:" "\nC:\Development\profile\aboutme.html"

How Tailwindcss uses String.raw:

ui.spec.ts test file assigns String.raw to html and css.

html is found to be used in a lot of tests written in ui.spec.ts

Let’s take a closer look at this test code:

for (let [classes, expected] of [
 [
 'bg-linear-to-r from-red-500',
 'linear-gradient(to right, rgb(239, 68, 68) 0%, rgba(0, 0, 0, 0) 100%)',
 ],
 [
 'bg-linear-to-r via-red-500',
 'linear-gradient(to right, rgba(0, 0, 0, 0) 0%, rgb(239, 68, 68) 50%, rgba(0, 0, 0, 0) 100%)',
 ],
 [
 'bg-linear-to-r to-red-500',
 'linear-gradient(to right, rgba(0, 0, 0, 0) 0%, rgb(239, 68, 68) 100%)',
 ],
 [
 'bg-linear-to-r from-red-500 to-blue-500',
 'linear-gradient(to right, rgb(239, 68, 68) 0%, rgb(59, 130, 246) 100%)',
 ],
 [
 'bg-linear-to-r via-red-500 to-blue-500',
 'linear-gradient(to right, rgba(0, 0, 0, 0) 0%, rgb(239, 68, 68) 50%, rgb(59, 130, 246) 100%)',
 ],
 [
 'bg-linear-to-r from-red-500 via-green-500 to-blue-500',
 'linear-gradient(to right, rgb(239, 68, 68) 0%, rgb(34, 197, 94) 50%, rgb(59, 130, 246) 100%)',
 ],
 [
 'bg-linear-[to_right,var( - color-red-500),var( - color-green-500),var( - color-blue-500)]',
 'linear-gradient(to right, rgb(239, 68, 68), rgb(34, 197, 94), rgb(59, 130, 246))',
 ],
]) {
 test(`background gradient, "${classes}"`, async ({ page }) => {
   let { getPropertyValue } = await render(
   page,
   html`<div id="x" class="${classes}">Hello world</div>`,
   )
   expect(await getPropertyValue('#x', 'background-image')).toEqual(expected)
 })
}

It is interesting to see an entire array defined with in a for loop.

html`<div id="x" class="${classes}">Hello world</div>`,

${classes} gets replaced with first item of the below array:

[
 'bg-linear-to-r from-red-500',
 'linear-gradient(to right, rgb(239, 68, 68) 0%, rgba(0, 0, 0, 0) 100%)',
],

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References:

1. https://github.com/tailwindlabs/tailwindcss/blob/next/packages/tailwindcss/tests/ui.spec.ts

2. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/raw

3. https://stackoverflow.com/questions/34772762/what-are-the-actual-uses-of-es6-raw-string-access