Squarespace Forms Integration for Salesforce

salesforce.js

Y.namespace('Template').Salesforce = Class.create({

  /*
    baseUrl
    oid
    sqsFormSubmit
  */
  initialize: function (config) {
    this.config = config;
  },

  submit: function () {
    var formData = this.getFormData(this.config.sqsFormSubmit);
    var phoneNumber = '';

    if (formData['phone'] && formData['phone'].length >= 4) {
      phoneNumber = formData['phone'].join('-');
    }
    var description = '';

    for (key in formData) {
      var value = formData[key];

      if (Array.isArray(value)) {
        value = value.join(' ');
      }

      description += key + ': ' + value + '\n';
    }

    var params = {
      first_name: formData['name'][0],
      last_name: formData['name'][1],
      email: formData['email_address'],
      phone: phoneNumber,
      company: formData['company'],
      lead_source: formData['sqf_lead_source'] || 'web',
      description: description,
      oid: this.config.oid
    };

    $.ajax({
      url: this.config.baseUrl,
      data: params,
      type: 'GET',
      dataType: 'jsonp',
      jsonp: false,
      complete: function(data) {
        debugger;
        console.log('done');
      }
    });
  },

  getFormData: function (formSubmit) {
    var data = {};

    formSubmit.get("formNode").all(".form-item").each(function(item) {
      var key = null;

      if (item.get('nodeName') == 'FIELDSET') {
        key = item.get('id').split('-')[0];
      } else {
        var inputNode = item.one('.title');

        if (inputNode) {
          var text = inputNode.get('innerText');
          key = text.replace(' *', '').replace(' ', "_").toLowerCase();
        } else {
          key = item._node.name.toLowerCase();
        }
      }

      if (key) {
        data[key] = formSubmit._getFieldData(item);
      }
    });

    return data;
  }

});

site.js

Y.on('domready', function() {
		Y.all('form').each(function(n) {
			// remove SQS form handler and get reference to form Id
			var onSubmitValue = n.getAttribute('onsubmit');
			var sqsFormId = onSubmitValue.match(/submit\('(.*)',/)[1];

			n.setAttribute('onsubmit', '');

			n.on('submit', function(e) {
				e.preventDefault();

      	Y.use('squarespace-form-submit', 'node', function (Y) {
      		var formSubmit = new Y.Squarespace.FormSubmit({ formNode: n });

      		formSubmit._submitSuccess = function () {
      			// Submit to sales force
      			var salesforce = new Y.Template.Salesforce({
	            baseUrl: "https://www.salesforce.com/servlet/servlet.WebToLead?encoding=UTF-8",
	            oid: "#################", // replace with your OID from Salesforce
	            sqsFormSubmit: formSubmit
	          });

	          salesforce.submit();

      			// Show message
      			var formNode = this.get("formNode");
      			var submitText = formNode.one(".form-submission-text").cloneNode(!0);
      			var submitHtml = formNode.one(".form-submission-html").cloneNode(!0);
      			var submitHtmlData = submitHtml.getData("submission-html");

      			submitHtml.setHTML(submitHtmlData);
      			submitHtml.removeClass("hidden");
      			submitText.removeClass("hidden");
      			formNode.empty();
      			formNode.append(submitText).append(submitHtml);
	      	};

      		formSubmit.submit(sqsFormId, sqsFormId);
      	});
      });
    });
	});

@jdshepard I got this to work in non-developer mode. Note my comments!
My forked solution

For any developers having trouble getting this to work, try changing the regular expression pattern for sqsFormId to:
/submit\('([^']*)',/