require file as string

The selected answer is deprecated and not recommended anymore. NodeJS documentation suggests other approaches like:

loading modules via some other Node.js program

but it does not expand any more.

• You can use a very simple library like this: require-text

• Or implement it yourself ( like from the package above: )

  var fs = require('fs');
  module.exports = function(name, require) {
     return fs.readFileSync(require.resolve(name)).toString();
  };
  

If it's for a (few) specific extension(s), you can add your own require.extensions handler:

var fs = require('fs');

require.extensions['.txt'] = function (module, filename) {
    module.exports = fs.readFileSync(filename, 'utf8');
};

var words = require("./words.txt");

console.log(typeof words); // string

Otherwise, you can mix fs.readFile with require.resolve:

var fs = require('fs');

function readModuleFile(path, callback) {
    try {
        var filename = require.resolve(path);
        fs.readFile(filename, 'utf8', callback);
    } catch (e) {
        callback(e);
    }
}

readModuleFile('./words.txt', function (err, words) {
    console.log(words);
});

To read the CSS file to String, use this code. It works for .txt.

const fs = require('fs')
const path = require('path')

const css = fs.readFileSync(path.resolve(__dirname, 'email.css'), 'utf8')

ES6:

import fs from 'fs'
import path from 'path'

let css = fs.readFileSync(path.resolve(__dirname, 'email.css'), 'utf8')