How to prepopulate fields on Standard layout? - Tooling API to the rescue

              Have you ever wondered populating a field's value while creating a new record on a standard detail page?
You can do so by assigning the value to field id. But how do I get the field Id? By grabbing the Id from Inspect Element? If so, then, how do you manage the field ids accross different Salesforce orgs/environments?

We have Tooling API to the rescue.

Use Tooling API when you need fine-grained access to an org’s metadata. Tooling API’s SOQL capabilities for many metadata types allow you to retrieve smaller pieces of metadata.

You can use Tooling API using REST/SOAP. We can also use these  Apex Wrappers & Javascript Wrappers(jsForce).

Thank you very much Andrew Fewcett, James Loghry & Shinchi Tomita for creating these wonderful wrappers! These are awesome, timesaving & very helpful!

Let's get into hands-on in retrieving the field id using JSForce library.

	<script src="https://cdnjs.cloudflare.com/ajax/libs/jsforce/1.6.0/jsforce-core.js"></script>
	<script src="https://cdnjs.cloudflare.com/ajax/libs/jsforce/1.6.0/jsforce-api-tooling.js"></script>
	function getFieldId(){
	var conn = new jsforce.Connection({ accessToken: "{!$API.Session_Id}" });
	var customObjectId = '';
	/* Retrieve CustomObject Id from DeveloperName.
	* As we are querying from CustomObject, we need not specify '__c'.
	*/
	conn.tooling.sobject('CustomObject').
	find({ DeveloperName: "Bug"},["Id","DeveloperName"]).execute(function(err, records) {
	if (err) { return console.error(err); }
	customObjectId = records.length > 0 ? records[0].Id : '';
	/* Query CustomField using CustomObjectId.
	* As we are querying from CustomField, we need not specify '__c'.
	*/
	conn.tooling.sobject('CustomField').
	find({ TableEnumOrId: customObjectId, DeveloperName : "Type"},["Id","DeveloperName"]).
	execute(function(err, records) {
	if (err) { return console.error(err); }
	var customFieldId = records.length > 0 ? records[0].Id.substring(0, 15) : '';
	console.log(customFieldId);
	});
	});
	}

view raw getFieldId.js hosted with ❤ by GitHub

In the above example, Bug is a custom object, and Type is a custom field in Bug. I am trying to retrieve the id of Type(CustomField) using Bug(CustomObject)  id.