example.js

var path = require('path')
var twig = require('node-twig')

var options = {
    extensions: [
        {
            file: path.join(__dirname, 'map.php'),
            func: 'mapForTwigExtension'
        }
    ],
    context: {
        state: 'TX'
    }
}

twig.renderFile(path.join(__dirname, 'test.twig'), options, (err, output) => {
    if (err) console.error(err)
    else console.log(output)
})

map.php

<?php

function mapForTwigExtension(\Twig_Environment &$twig) {
    $twig->addFilter(
        new \Twig_Filter('map',
            function ($text, $map, $default = null) {
                // If map has a key matching $text, return its mapped value
                if (isset($map[$text])) {
                    return $map[$text];
                }

                // Otherwise, if a default was specified, return it
                if (null !== $default) {
                    return $default;
                }

                // Otherwise, return the original value
                return $text;
            }
        )
    );
}

test.twig

So, you're from {{ state | map({ "TX":"Texas", "LA":"Louisiana" }, "WHERE exactly?") }}