Pre-building Indexes

For large numbers of documents, it can take time for Lunr to build an index. The time taken to build the index can lead a browser to block; making your site seem unresponsive.

A better way is to pre-build the index, and serve a serialised index that Lunr can load on the client side much quicker.

This technique is useful with large indexes, or with documents that are largely static, such as with a static website.


Lunr indexes support serialisation in JSON. Assuming that the index has already been created, it be serialised using the built-in JSON object:

var serializedIdx = JSON.stringify(idx)

This serialized index can then be written to a file, compressed, and served along side other static assets.

The below example is a script that can be used to build a serialised index. It assumes that the documents will be available in JSON format on STDIN, and have fields title and body and a ref of id.

var lunr = require('lunr'),
    stdin = process.stdin,
    stdout = process.stdout,
    buffer = []


stdin.on('data', function (data) {

stdin.on('end', function () {
  var documents = JSON.parse(buffer.join(''))

  var idx = lunr(function () {

    documents.forEach(function (doc) {
    }, this)


Assuming that the above script is in a file called build-index.js in the current directory, it can be used to create a serialised index with JSON from STDIN:

$ echo '[{ "id": "1", "title": "Foo", "body": "Bar" }]' | node build-index.js > index.json


Loading a serialised index is significantly quicker than building the index from scratch. Assuming a variable named data contains the serialised index, loading the index is done like this:

var idx = lunr.Index.load(JSON.parse(data))