115 lines
3.4 KiB
JavaScript
115 lines
3.4 KiB
JavaScript
/**
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* @license Apache-2.0
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*
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* Copyright (c) 2019 The Stdlib Authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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'use strict';
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// MODULES //
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var isObject = require( '@stdlib/assert/is-object' );
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var isFunction = require( '@stdlib/assert/is-function' );
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var defineProperty = require( './../../define-property' );
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// MAIN //
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/**
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* Defines a memoized object property.
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*
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* @param {Object} obj - object on which to define the property
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* @param {(string|symbol)} prop - property name
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* @param {Object} desc - property descriptor
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* @param {boolean} [desc.configurable=false] - boolean indicating if the property descriptor can be changed and if the property can be deleted from the provided object
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* @param {boolean} [desc.enumerable=false] - boolean indicating if the property shows up when enumerating object properties
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* @param {boolean} [desc.writable=false] - boolean indicating if the value associated with the property can be changed with an assignment operator
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* @param {Function} desc.value - function whose return value will be memoized
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* @throws {TypeError} first argument must be an object
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* @throws {TypeError} third argument must be an object
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* @throws {TypeError} property descriptor `value` property must be a function
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*
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* @example
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* var obj = {};
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*
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* function foo() {
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* return 'bar';
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* }
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*
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* defineMemoizedProperty( obj, 'foo', {
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* 'configurable': false,
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* 'enumerable': false,
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* 'writable': false,
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* 'value': foo
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* });
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*
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* var v = obj.foo;
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* // returns 'bar'
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*/
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function defineMemoizedProperty( obj, prop, desc ) {
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if ( !isObject( obj ) ) {
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throw new TypeError( 'invalid argument. First argument must be an object. Value: `' + obj + '`.' );
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}
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if ( !isObject( desc ) ) {
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throw new TypeError( 'invalid argument. Property descriptor must be an object. Value: `' + desc + '`.' );
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}
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if ( !isFunction( desc.value ) ) {
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throw new TypeError( 'invalid argument. The `value` property of the property descriptor must be a function. Value: `' + desc.value + '`.' );
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}
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// Copy descriptor properties to a new data descriptor object:
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desc = {
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'configurable': ( desc.configurable === void 0 ) ? false : desc.configurable,
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'enumerable': ( desc.enumerable === void 0 ) ? false : desc.enumerable,
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'writable': ( desc.writable === void 0 ) ? false : desc.writable,
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'value': desc.value
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};
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// Define a configurable (at least temporarily) accessor property:
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defineProperty( obj, prop, {
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'configurable': true,
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'enumerable': desc.enumerable,
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'get': getter,
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'set': ( desc.writable ) ? memoize : void 0
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});
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/**
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* Temporary get accessor.
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*
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* @private
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* @returns {*} property value
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*/
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function getter() {
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var value = desc.value.call( obj );
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memoize( value );
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return value;
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}
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/**
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* Defines a memoized object property.
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*
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* @private
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* @param {*} value - value to set
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*/
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function memoize( value ) {
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desc.value = value;
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defineProperty( obj, prop, desc );
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}
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}
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// EXPORTS //
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module.exports = defineMemoizedProperty;
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