How can I add a search box to a map that allows users to search>zoom to a polygon name?
So, if there are 100 polygons, the user would be able to type the name of the polygon (i.e., Symantec), then the map would zoom to the matching county.
[GIS] Search and zoom json features in Leaflet
jsonleafletmapboxsearch
Related Solutions
You could use the Leaflet search control. It allows you to insert a search widget on your map, search by place names around the world (see Nominatim example), and once a place is selected, zoom/center your map to that place location.
In the Leaflet search's GitHub website you find examples on how to add the control to your leaflet map.
Since your question changed and I misread the server answer somehow, it is much easier now and you can refer to the official Leaflet documentation and don't need to use Proj4Leaflet at all to do this task.
How to display the geojson result and zoom to it:
let parcelLayer = L.geoJSON(parcel).addTo(map);
map.fitBounds(parcelLayer.getBounds());
For the search box there are a couple of ways you can do it, but basically you need to get the value from a input field and then modify the input similar to the following example:
var searchInput = document.getElementById("search").value;
var baseInspireId = "FR291550000";
var letter = searchInput.substring(0,1);
var digits = searchInput.substring(1);
// add the maximum possible numbers of zeros
digits = "000"+digits;
// take only the last four digits
digits = digits.substring(digits.length-4);
var result = baseInspireId + letter + digits;
Best Answer
There are various solutions for this (if you don't want exact zoom but centering). You can use using the list from Leaflet plugins page:
You can also take a look on the Bootleaf project, a Bootstrap based Leaflet template using typehead.js (an autocomplete search box).
All the mentioned projects above have demos available so you can check if it's the expected solution for you.