After looking at another answer it would seem I need to also pass id field with every call, otherwise it will disable the input.

Sample code that fixed it:

$('.select2').select2({  placeholder: "Policy Name",  minimumInputLength: 3,  multiple: false,  quietMillis: 100,  id: function(bond){ return bond._id; },  ajax: {    url: "http://localhost:3000/search",    dataType: 'json',    type: 'POST',    data: function(term, page) {      return {        search: term,        page: page || 1      }    },    results: function(bond, page) {      return {results: bond.results, more: (bond.results && bond.results.length == 10 ? true: false)}    }  },  formatResult: formatResult,  formatSelection: formatSelection,  initSelection: initSelection})

Edit

Since this keeps getting upvoted I'll elaborate a bit. The .select2() method expects a unique id field on all results. Thankfully, there's a workaround. The id option accepts a function like this:

function( <INDIVIDUAL_RESULT> ) {  // Expects you to return a unique identifier.  // Ideally this should be from the results of the $.ajax() call. }

Since my unique identifier was <RESULT>._id, I simply return <RESULT>._id;

The thing is that the JSON data need a property called "id". There's no need for

id: function(bond){ return bond._id; }

If the data does not have an id for itself, you can add it with a function on processResults like here.

        $(YOUR FIELD).select2({            placeholder: "Start typing...",            ajax: {                type: "POST",                contentType: "application/json; charset=utf-8",                url: "YOUR API ENDPOINT",                dataType: 'json',                data:                     function (params) {                        return JSON.stringify({ username: params.term });                },                processResults: function (data, page) {                    var results = [];                    $.each(JSON.parse(data.d), function (i, v) {                        var o = {};                        o.id = v.key;                        o.name = v.displayName;                        o.value = v.key;                        results.push(o);                    })                    return {                        results: results                    };                },                cache: true            },            escapeMarkup: function (markup) { return markup;},            minimumInputLength: 1,            templateResult: function (people) {                if (people.loading)                    return people.text;                var markup = '<option value="' + people.value + '">' + people.name + '</option>';                return markup;            },            templateSelection: function (people) { return people.value || people.text }        });    

Also be careful with the case. I was using Id but select2 expects id. Could save someone's time.