A middleware for Express that allows for stream-based string replacement before sending responses.

Install in your Express project using:

npm install --save string-replace-middleware

After installing, you can add it as a middleware to your project and hand over a map of replacements. To replace every occurence of foo with bar.

const express = require('express');
const { stringReplace } = require('string-replace-middleware');

const app = express();

app.use(stringReplace({
    'foo': 'bar',
}));

app.listen(3000);

Use it to serve static files with replacements like in this example:

const express = require('express');
const serveStatic = require('serve-static');
const { stringReplace } = require('string-replace-middleware');

const app = express();

app.use(stringReplace({
    'foo': 'bar',
}));
app.use(serveStatic('public'));

app.listen(3000);

You might also replace dynamically with access to all the content of Request and Response:

stringReplace({
    '$host' => (req, res) => 'your host ' + req.hostname
});

The Content-Type header of responses is checked against a regex before modification. The regex is configurable by passing in an options object like this:

const options = {
  contentTypeFilterRegexp: /^text\/|^application\/json$|^application\/xml$/,
}

app.use(stringReplace({
    'foo': 'bar',
}, options));

The default regex is /^text\/|^application\/json$|^application\/xml$/, which will match text/*, application/json, and application/xml. Any response with a Content-Type header that doesn't match the regex is ignored and passed-through without modification.

Also any response without a Content-Type header is ignored and passed-through without any modification.