A sample showing how to use "JSOM-based provisioning" to bind taxonomy fields in SharePoint/Office 365.

JsomProvisioning_TaxonomyFields.js

'use strict';
window.COB = window.COB || {};

window.COB.TermSetName = "Countries";
window.COB.TermSetLocale = "1033";
window.COB.FieldInternalName = "COB_Countries";

window.COB.JsomProvisioning = function () {
    var context,
        termStore,
        termSets,
        termSet,
        termSetName,
        fieldInternalName,
        termSetLocale,
        field,
        taxField,
        dialog,
        dialogTitle = "Please wait",
        dialogMessage = "We are getting your site ready..",
        dialogHeight = 500,
        dialogWidth = 500,

    initTaxObjects = function (fieldToBindInternalName, termSetToBindName, termSetToBindLocale) {
        console.log("In window.COB.JsomProvisioning.initTaxObjects()..");

        fieldInternalName = fieldToBindInternalName;
        termSetName = termSetToBindName;
        termSetLocale = termSetToBindLocale;

        // show dialog during execution of our provisioning steps..
        dialog = SP.UI.ModalDialog.showWaitScreenWithNoClose(dialogTitle, dialogMessage, dialogHeight, dialogWidth);

        $('#jsomProvisioningMessage').append("<br /><div>Attempting to fetch term set '" + termSetName + "' and field '" + fieldInternalName + "'.");

        context = SP.ClientContext.get_current();
        var taxonomySession = SP.Taxonomy.TaxonomySession.getTaxonomySession(context);
        context.load(taxonomySession);

        termStore = taxonomySession.getDefaultSiteCollectionTermStore();
        termSets = taxonomySession.getTermSetsByName(termSetName, termSetLocale);
        context.load(termStore);
        context.load(termSets);

        field = context.get_site().get_rootWeb().get_fields().getByInternalNameOrTitle(fieldInternalName);
        context.load(field);
        context.executeQueryAsync(onInitTaxObjectsSuccess, onInitTaxObjectsFail);
    },
    onInitTaxObjectsSuccess = function () {
        console.log("In window.COB.JsomProvisioning.onInitTaxObjectsSuccess()..");

        var termSetEnumerator = termSets.getEnumerator();
        
        while (termSetEnumerator.moveNext()) {
            var currentTermSet = termSetEnumerator.get_current();
            var currentTermSetName = currentTermSet.get_name();
            if (currentTermSetName === termSetName) {
                console.log("Found term set " + termSetName);
                termSet = currentTermSet;
            }
        }

        if (termSet != undefined) {
            console.log("Term set identified, proceeding..");
            bindTaxonomyField()
        }
        else {
            var msg = "Failed to find term set '" + termSetName + "'. Please check this exists in your Term Store!";
            console.log(msg);
            $('#jsomProvisioningMessage').append(msg);
            if (dialog != null) {
                dialog.close();
            }
        }
    },
    onInitTaxObjectsFail = function (sender, args) {
        alert('Failed to initialise taxonomy objects! Error:' + sender.statusCode);
    },

    bindTaxonomyField = function () {
        console.log("In window.COB.JsomProvisioning.bindTaxonomyField()..");

        taxField = context.castTo(field, SP.Taxonomy.TaxonomyField);
        taxField.set_sspId(termStore.get_id().toString());
        taxField.set_termSetId(termSet.get_id());

        taxField.updateAndPushChanges(true);
        context.executeQueryAsync(onBindTaxFieldSuccess, onBindTaxFieldFail);
    },
    onBindTaxFieldSuccess = function () {
        console.log("In window.COB.JsomProvisioning.onBindTaxFieldSuccess()..");
        // now we need to close the dialog, BUT I'm pausing for 4 seconds here for demo purposes using setTimeout() - things go too 
        // fast otherwise. The setTimeout() should be removed in real use.. 
        setTimeout(function () {
            $('#jsomProvisioningMessage').append('<br /><div>Taxonomy field bound successfully..</div>');
            if (dialog != null) {
                dialog.close();
            }
        }, 4000);
    },
    onBindTaxFieldFail = function (sender, args) {
        if (dialog != null) {
            dialog.close();
        }
        alert('Failed to bind taxonomy field! Error:' + sender.statusCode);
    }

    return {
        execute: function () {
            console.log("In window.COB.JsomProvisioning.execute()..");

            SP.SOD.executeFunc('sp.js', 'SP.ClientContext', function () {
                console.log("Loaded sp.js");
                SP.SOD.registerSod('sp.taxonomy.js', SP.Utilities.Utility.getLayoutsPageUrl('sp.taxonomy.js'));
                SP.SOD.executeFunc('sp.taxonomy.js', 'SP.Taxonomy.TaxonomySession', function () {
                    console.log("Loaded sp.taxonomy.js");
                    SP.SOD.executeFunc('sp.ui.dialog.js', 'SP.UI.ModalDialog.showWaitScreenWithNoClose', function () {
                        console.log("Loaded all files..");
                        initTaxObjects(window.COB.FieldInternalName, window.COB.TermSetName, window.COB.TermSetLocale);
                    });
                });
            });
        }
    }
}();

Hi Chris,
I wonder if you have the code for creating field as part of this. On line 24, the field was passed in. I have been struggling with creating taxonomy site column. I would greatly appreciate if you could give me some recommendations. Thanks SO much, Chris.

function createTaxonomyFieldInHost(hostUrl, groupNm, fieldNm, displayNm) {
_hostwebUrl = hostUrl;
_fieldName = fieldNm;

    var xmlDef = "<Field Type='TaxonomyFieldType' Name='";
    xmlDef += _fieldName + "' DisplayName='" + displayNm;
    xmlDef += "' Required='TRUE' Group='" + groupNm;
    xmlDef += "' ID='{bed14299-afe0-4c75-9e04-92e3d8b39a18}'>";

    _hostwebContext = new SP.ClientContext(_hostwebUrl);
    var newField = _hostwebContext.get_web().get_fields().addFieldAsXml(xmlDef, false, SP.AddFieldOptions.ddToNoContentType);
    _hostwebContext.load(newField);
    _hostwebContext.executeQueryAsync(successCreatedTaxonomyField, errorCreatedTaxonomyField);

}

//Success Create a field
function successCreatedTaxonomyField(data) {
var msg = "";
msg += _fieldName + "";

    $('#lblResultField').html("<b>successfully created Taxonomy Field! </b>" + msg);
}

//Error creating a field
function errorCreatedTaxonomyField(data, errorCode, errorMessage) {
    $('#lblResultField').html("Could not complete create Taxonomy Field: " + errorMessage);
}