feat: add format support

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---

Author: kgryte

lib/node_modules/@stdlib/plot/vega/axis/ctor/lib/format/get.js

@@ -0,0 +1,46 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2025 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';
+
+// MODULES //
+
+var isObject = require( '@stdlib/assert/is-object' );
+var objectAssignIn = require( '@stdlib/object/assign-in' );
+var prop = require( './properties.js' );
+
+
+// MAIN //
+
+/**
+* Returns a format specifier for axis tick labels.
+*
+* @private
+* @returns {(string|Object|void)} format specifier
+*/
+function get() {
+	var v = this[ prop.private ];
+	return ( isObject( v ) ) ? objectAssignIn( {}, v ) : v;
+}
+
+
+// EXPORTS //
+
+module.exports = get;

lib/node_modules/@stdlib/plot/vega/axis/ctor/lib/format/properties.js

@@ -0,0 +1,33 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2025 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 property2object = require( '@stdlib/plot/vega/base/property2object' );
+
+
+// MAIN //
+
+var obj = property2object( 'format' );
+
+
+// EXPORTS //
+
+module.exports = obj;

lib/node_modules/@stdlib/plot/vega/axis/ctor/lib/format/set.js

@@ -0,0 +1,75 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2025 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';
+
+// MODULES //
+
+var logger = require( 'debug' );
+var isObject = require( '@stdlib/assert/is-object' );
+var isString = require( '@stdlib/assert/is-string' ).isPrimitive;
+var isUndefined = require( '@stdlib/assert/is-undefined' );
+var objectAssignIn = require( '@stdlib/object/assign-in' );
+var format = require( '@stdlib/string/format' );
+var changeEvent = require( './../change_event.js' );
+var prop = require( './properties.js' );
+
+
+// VARIABLES //
+
+var debug = logger( 'vega:axis:set:'+prop.name );
+
+
+// MAIN //
+
+/**
+* Sets a format specifier for axis tick labels.
+*
+* ## Notes
+*
+* -   Providing `undefined` "unsets" the configured value.
+*
+* @private
+* @param {(string|Object|void)} value - input value
+* @throws {TypeError} must be a string or valid format object
+* @returns {void}
+*/
+function set( value ) {
+	var isObj = isObject( value );
+
+	// FIXME: validate that an object is a valid TimeMultiFormat object
+
+	if ( !isObj && !isString( value ) && !isUndefined( value ) ) {
+		throw new TypeError( format( 'invalid assignment. `%s` must be a string or a valid format object. Value: `%s`.', prop.name, value ) );
+	}
+
+	// TODO: consider a deep equality check for format objects in order to avoid false positive change events
+
+	if ( value !== this[ prop.private ] ) {
+		debug( 'Current value: %s. New value: %s.', JSON.stringify( this[ prop.private ] ), JSON.stringify( value ) );
+		this[ prop.private ] = ( isObj ) ? objectAssignIn( {}, value ) : value;
+		this.emit( 'change', changeEvent( prop.name ) );
+	}
+}
+
+
+// EXPORTS //
+
+module.exports = set;

lib/node_modules/@stdlib/plot/vega/axis/ctor/lib/main.js

@@ -62,6 +62,9 @@ var setDomainOpacity = require( './domain-opacity/set.js' );
 var getDomainWidth = require( './domain-width/get.js' );
 var setDomainWidth = require( './domain-width/set.js' );
 
+var getFormat = require( './format/get.js' );
+var setFormat = require( './format/set.js' );
+
 var getGrid = require( './grid/get.js' );
 var setGrid = require( './grid/set.js' );
 var getGridCap = require( './grid-cap/get.js' );
@@ -519,6 +522,25 @@ setReadWriteAccessor( Axis.prototype, 'domainDashOffset', getDomainDashOffset, s
 */
 setReadWriteAccessor( Axis.prototype, 'domainOpacity', getDomainOpacity, setDomainOpacity );
 
+/**
+* Format specifier for axis tick labels.
+*
+* @name format
+* @memberof Axis.prototype
+* @type {(void|string|Object)}
+*
+* @example
+* var axis = new Axis({
+*     'scale': 'xScale',
+*     'orient': 'bottom',
+*     'format': '%d'
+* });
+*
+* var v = axis.format;
+* // returns '%d'
+*/
+setReadWriteAccessor( Axis.prototype, 'format', getFormat, setFormat );
+
 /**
 * Stroke width of an axis domain line.
 *