feat: add plot/vega/signal/reference

PR-URL: #10564
Co-authored-by: Athan Reines <kgryte@gmail.com>
Reviewed-by: Athan Reines <kgryte@gmail.com>

Author: gururaj1512

lib/node_modules/@stdlib/plot/vega/signal/reference/examples/index.js

@@ -0,0 +1,29 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2026 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*    http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+'use strict';
+
+var SignalReference = require( './../lib' );
+
+var signal = new SignalReference( 'width' );
+console.log( signal.toJSON() );
+// => { 'signal': 'width' }
+
+signal = new SignalReference( 'width / 2' );
+console.log( signal.toJSON() );
+// => { 'signal': 'width / 2' }

lib/node_modules/@stdlib/plot/vega/signal/reference/lib/change_event.js

@@ -0,0 +1,41 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2026 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*    http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+'use strict';
+
+// MAIN //
+
+/**
+* Returns a new change event object.
+*
+* @private
+* @param {string} property - property name
+* @returns {Object} event object
+*/
+function event( property ) { // eslint-disable-line stdlib/no-redeclare
+	return {
+		'type': 'update',
+		'source': 'signal-reference',
+		'property': property
+	};
+}
+
+
+// EXPORTS //
+
+module.exports = event;

lib/node_modules/@stdlib/plot/vega/signal/reference/lib/index.js

@@ -0,0 +1,40 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2026 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*    http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+'use strict';
+
+/**
+* Signal reference constructor.
+*
+* @module @stdlib/plot/vega/signal/reference
+*
+* @example
+* var SignalReference = require( '@stdlib/plot/vega/signal/reference' );
+*
+* var signal = new SignalReference( 'width' );
+* // returns <SignalReference>
+*/
+
+// MODULES //
+
+var main = require( './main.js' );
+
+
+// EXPORTS //
+
+module.exports = main;

lib/node_modules/@stdlib/plot/vega/signal/reference/lib/main.js

@@ -0,0 +1,164 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2026 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*    http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+/* eslint-disable no-restricted-syntax, no-invalid-this */
+
+'use strict';
+
+// MODULES //
+
+var EventEmitter = require( 'events' ).EventEmitter;
+var logger = require( 'debug' );
+var isString = require( '@stdlib/assert/is-string' ).isPrimitive;
+var setNonEnumerableReadOnly = require( '@stdlib/utils/define-nonenumerable-read-only-property' );
+var setNonEnumerableReadOnlyAccessor = require( '@stdlib/utils/define-nonenumerable-read-only-accessor' ); // eslint-disable-line id-length
+var setReadWriteAccessor = require( '@stdlib/utils/define-read-write-accessor' );
+var inherit = require( '@stdlib/utils/inherit' );
+var instance2json = require( '@stdlib/plot/vega/base/to-json' );
+var transformErrorMessage = require( '@stdlib/plot/vega/base/transform-validation-message' );
+var format = require( '@stdlib/string/format' );
+var properties = require( './properties.json' );
+
+// Note: keep the following in alphabetical order according to the `require` path...
+var getProperties = require( './properties/get.js' );
+
+var getSignal = require( './signal/get.js' );
+var setSignal = require( './signal/set.js' );
+
+
+// VARIABLES //
+
+var debug = logger( 'vega:signal-reference:main' );
+
+
+// MAIN //
+
+/**
+* Signal reference constructor.
+*
+* @constructor
+* @param {string} reference - signal reference string
+* @throws {TypeError} must provide a string
+* @throws {Error} must provide valid arguments
+* @returns {SignalReference} signal reference instance
+*
+* @example
+* var signal = new SignalReference( 'width' );
+* // returns <SignalReference>
+*
+* @example
+* var signal = new SignalReference( 'width / 2' );
+* // returns <SignalReference>
+*/
+function SignalReference( reference ) {
+	if ( !( this instanceof SignalReference ) ) {
+		return new SignalReference( reference );
+	}
+	EventEmitter.call( this );
+	if ( !isString( reference ) ) {
+		throw new TypeError( format( 'invalid argument. Must provide a string. Value: `%s`.', reference ) );
+	}
+	try {
+		this.signal = reference;
+	} catch ( err ) {
+		debug( 'Encountered an error. Error: %s', err.message );
+
+		// FIXME: retain thrown error type
+		throw new Error( transformErrorMessage( err.message ) );
+	}
+	return this;
+}
+
+/*
+* Inherit from the `EventEmitter` prototype.
+*/
+inherit( SignalReference, EventEmitter );
+
+/**
+* Constructor name.
+*
+* @private
+* @name name
+* @memberof SignalReference
+* @readonly
+* @type {string}
+*/
+setNonEnumerableReadOnly( SignalReference, 'name', 'SignalReference' );
+
+/**
+* Signal reference string.
+*
+* @name signal
+* @memberof SignalReference.prototype
+* @type {string}
+*
+* @example
+* var signal = new SignalReference( 'width' );
+*
+* var v = signal.signal;
+* // returns 'width'
+*
+* @example
+* var signal = new SignalReference( 'width / 2' );
+*
+* var v = signal.signal;
+* // returns 'width / 2'
+*/
+setReadWriteAccessor( SignalReference.prototype, 'signal', getSignal, setSignal );
+
+/**
+* Signal reference properties.
+*
+* @name properties
+* @memberof SignalReference.prototype
+* @type {Array<string>}
+*
+* @example
+* var signal = new SignalReference( 'width' );
+*
+* var v = signal.properties;
+* // returns [...]
+*/
+setNonEnumerableReadOnlyAccessor( SignalReference.prototype, 'properties', getProperties );
+
+/**
+* Serializes an instance to a JSON object.
+*
+* ## Notes
+*
+* -   This method is implicitly invoked by `JSON.stringify`.
+*
+* @name toJSON
+* @memberof SignalReference.prototype
+* @type {Function}
+* @returns {Object} JSON object
+*
+* @example
+* var signal = new SignalReference( 'width' );
+*
+* var v = signal.toJSON();
+* // returns { 'signal': 'width' }
+*/
+setNonEnumerableReadOnly( SignalReference.prototype, 'toJSON', function toJSON() {
+	return instance2json( this, properties );
+});
+
+
+// EXPORTS //
+
+module.exports = SignalReference;

lib/node_modules/@stdlib/plot/vega/signal/reference/lib/properties.json

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+[
+  "signal"
+]

lib/node_modules/@stdlib/plot/vega/signal/reference/lib/properties/get.js

@@ -0,0 +1,41 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2026 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*    http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+'use strict';
+
+// MODULES //
+
+var properties = require( './../properties.json' );
+
+
+// MAIN //
+
+/**
+* Returns the list of enumerable properties.
+*
+* @private
+* @returns {Array<string>} properties
+*/
+function get() {
+	return properties.slice();
+}
+
+
+// EXPORTS //
+
+module.exports = get;

lib/node_modules/@stdlib/plot/vega/signal/reference/lib/signal/get.js

@@ -0,0 +1,43 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2026 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*    http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+/* eslint-disable no-invalid-this */
+
+'use strict';
+
+// VARIABLES //
+
+var prop = require( './properties.js' );
+
+
+// MAIN //
+
+/**
+* Returns the signal reference.
+*
+* @private
+* @returns {string} signal reference
+*/
+function get() {
+	return this[ prop.private ];
+}
+
+
+// EXPORTS //
+
+module.exports = get;