deleteReadOnlyField.js

/** Script configuration goes here */
var LIST_TITLE = 'YOUR LIST TITLE HERE';
var FIELD_NAME = 'YOUR FIELD NAME HERE';

/** Actual logic used to list the field names. */
(function (listTitle, readOnlyField) {

	// First grab our client context.
	var oCtx = SP.ClientContext.get_current(),

	// Cache stuff to prevent needlessly recomputing stuff.
	oList = oCtx.get_web().get_lists().getByTitle(listTitle),
	oField = oList.get_fields().getByInternalNameOrTitle(readOnlyField);

	// Entrypoint
	deleteReadOnlyField(oField, function () {
		alert('Field successfully removed!');
	});
	
	/// #region Actual Logic

	function deleteReadOnlyField(oField, onSuccess) {
		// Set the "ReadOnly" property to false
		oField.set_readOnlyField(false);

		// Register the changes.
		oField.update()
		oCtx.load(oField);
		
		// Execute our query. If the property change made to our field was
		// successful, we can delete the field and finish up.
		executeQuery(this, function() {
			oField.deleteObject();
			executeQuery(this, onSuccess, 'DeleteField');
		}, 'SetReadOnly=False');
	}

	/// #endregion


	/// #region Utility Functions

	function isDefined(subject) {
		// Self-explanatory
		return typeof(subject[member]) !== 'undefined';
	}

	function hasMember(subject, member) {
		// subject has a specific member (value of member can be null, just
		// so long as it exists)
		return subject &&
		Object.prototype.hasOwnProperty.call(subject, member) ||
		isDefined(subject[member])
	}

	/** Show a generic error message */
	function showError(description, args) {
		// Show error message prefixed with the "description" parameter.
		alert('Error occurred ' + prefix + ': '
			 + args.get_message() + '\n'
			 + args.get_stackTrace()); // lazy
	}

	/** Have the context execute all pending operations. */
	function executeQuery(self, onSuccess, onError) {
		// If onError is a string value, generate a call to showError, using
		// the string for its description field.
		if (typeof(onError) === 'string' || (onError instanceof String)) {
			var description = onError;
			onError = function (sender, args) {
				showError.call(this, description, args);
			};
		}

		return oCtx.executeQueryAsync(
			Function.createDelegate(self, onSuccess),
			Function.createDelegate(self, onError || showError));
	}

	/// #endregion

})(LIST_TITLE, FIELD_NAME);