From 218934fa2ed1c702a6d3923d2aa2cc6b43c48684 Mon Sep 17 00:00:00 2001 From: Peter Bengtsson Date: Tue, 8 Dec 2020 14:43:23 -0500 Subject: initial commit --- files/uk/web/javascript/data_structures/index.html | 305 +++++++++++++++++++++ 1 file changed, 305 insertions(+) create mode 100644 files/uk/web/javascript/data_structures/index.html (limited to 'files/uk/web/javascript/data_structures') diff --git a/files/uk/web/javascript/data_structures/index.html b/files/uk/web/javascript/data_structures/index.html new file mode 100644 index 0000000000..ae52c4dbdc --- /dev/null +++ b/files/uk/web/javascript/data_structures/index.html @@ -0,0 +1,305 @@ +--- +title: Типи та структури даних у JavaScript +slug: Web/JavaScript/Data_structures +tags: + - JavaScript + - Types +translation_of: Web/JavaScript/Data_structures +--- +
{{jsSidebar("More")}}
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Усі мови програмування мають вбудовані структури даних, які, втім, у різних мовах дещо відрізняються. У цій статті ми розглянемо наявні у JavaScript структури даних та їх властивості, а також створення на їх основі інших структур. За можливості наведемо порівняння з іншими мовами.

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Динамічна типізація

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JavaScript є мовою з нестрогою типізацією або ж динамічною мовою. Оголошення змінної в JavaScript не визначає типу даних, а отже всяка змінна з отриманням нового значення отримує і новий тип. Звідси випливає, що тип з'ясовується перед виконанням певної операції, позаяк від нього залежить і результат:

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// Одразу по оголошенню змінна foo разом з початковим значенням отримує тип Number
+var foo = 42;
+
+console.log(foo + 1);  // виводить 43
+
+// Змінна отримує нове значення й тепер має тип String
+foo = 'bar';
+
+console.log(foo + 1);  // виводить "bar1"
+
+// Разом із значенням true тип змінної foo обертається на Boolean
+foo = true;
+
+ +

Типи даних

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Згідно з останнім стандартом ECMAScript у мові є сім типів даних:

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Прості величини

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Усі типи даних, окрім об'єкта, передають незмінювані величини (можна встановити нове значення змінної, але неможливо змінити того значення, яке вона вже має). На відміну від, наприклад, мови C, рядки є незмінюваними. Такі величини називають {{Glossary("Primitive", "простими")}} або «примітивними».

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Тип boolean

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Тип Boolean передає два логічних значення: true та false.

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Тип null

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Тип Null, власне, передає лише одне-єдине значення: null. Див. також {{jsxref("null")}} та {{Glossary("Null")}}.

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Тип undefined

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Змінна, допоки не отримає нового (початкового), має значення undefined. Див. також {{jsxref("Global_Objects/undefined", "undefined")}} та {{Glossary("Undefined")}}.

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Тип number

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Відповідно до стандарту ECMAScript, існує лише один тип чисел: 64-розрядне число подвійної точності з рухомою комою в форматі IEEE 754 (приймає значення від -(253 -1) до 253 -1). Для цілих чисел немає окремого типу даних. Окрім чисел з рухомою комою цей формат підтримує три особливих значення: +Infinity, -Infinity та {{jsxref("Global_Objects/NaN", "NaN")}} (так зване «не число»).

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To check for the largest available value or smallest available value within +/-Infinity, you can use the constants {{jsxref("Number.MAX_VALUE")}} or {{jsxref("Number.MIN_VALUE")}} and starting with ECMAScript 6, you are also able to check if a number is in the double-precision floating-point number range using {{jsxref("Number.isSafeInteger()")}} as well as {{jsxref("Number.MAX_SAFE_INTEGER")}} and {{jsxref("Number.MIN_SAFE_INTEGER")}}. Beyond this range, integers in JavaScript are not safe anymore and will be a double-precision floating point approximation of the value.

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The number type has only one integer that has two representations: 0 is represented as -0 and +0. ("0" is an alias for +0). In the praxis, this has almost no impact. For example +0 === -0 is true. However, you are able to notice this when you divide by zero:

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> 42 / +0
+Infinity
+> 42 / -0
+-Infinity
+
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Although a number often represents only its value, JavaScript provides some binary operators. These can be used to represent several Boolean values within a single number using bit masking. However, this is usually considered a bad practice, since JavaScript offers other means to represent a set of Booleans (like an array of Booleans or an object with Boolean values assigned to named properties). Bit masking also tends to make code more difficult to read, understand, and maintain. It may be necessary to use such techniques in very constrained environments, like when trying to cope with the storage limitation of local storage or in extreme cases when each bit over the network counts. This technique should only be considered when it is the last measure that can be taken to optimize size.

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Тип string

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JavaScript's {{jsxref("Global_Objects/String", "String")}} type is used to represent textual data. It is a set of "elements" of 16-bit unsigned integer values. Each element in the String occupies a position in the String. The first element is at index 0, the next at index 1, and so on. The length of a String is the number of elements in it.

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Unlike in languages like C, JavaScript strings are immutable. This means that once a string is created, it is not possible to modify it. However, it is still possible to create another string based on an operation on the original string. For example:

+ + + +

Beware of "stringly-typing" your code!

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It can be tempting to use strings to represent complex data. Doing this comes with short-term benefits:

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With conventions, it is possible to represent any data structure in a string. This does not make it a good idea. For instance, with a separator, one could emulate a list (while a JavaScript array would be more suitable). Unfortunately, when the separator is used in one of the "list" elements, then, the list is broken. An escape character can be chosen, etc. All of this requires conventions and creates an unnecessary maintenance burden.

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Use strings for textual data. When representing complex data, parse strings and use the appropriate abstraction.

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Тип symbol

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Symbols are new to JavaScript in ECMAScript Edition 6. A Symbol is a unique and immutable primitive value and may be used as the key of an Object property (see below). In some programming languages, Symbols are called atoms. For more details see {{Glossary("Symbol")}} and the {{jsxref("Symbol")}} object wrapper in JavaScript.

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Об'єкти

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In computer science, an object is a value in memory which is possibly referenced by an {{Glossary("Identifier", "identifier")}}.

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Properties

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In JavaScript, objects can be seen as a collection of properties. With the object literal syntax, a limited set of properties are initialized; then properties can be added and removed. Property values can be values of any type, including other objects, which enables building complex data structures. Properties are identified using key values. A key value is either a String or a Symbol value.

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There are two types of object properties which have certain attributes: The data property and the accessor property.

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Data property

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Associates a key with a value and has the following attributes:

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Attributes of a data property
AttributeTypeDescriptionDefault value
[[Value]]Any JavaScript typeThe value retrieved by a get access of the property.undefined
[[Writable]]BooleanIf false, the property's [[Value]] can't be changed.false
[[Enumerable]]BooleanIf true, the property will be enumerated in for...in loops. See also Enumerability and ownership of propertiesfalse
[[Configurable]]BooleanIf false, the property can't be deleted and attributes other than [[Value]] and [[Writable]] can't be changed.false
+ + + + + + + + + + + + + + + + + + + + + + + + + +
Obsolete attributes (as of ECMAScript 3, renamed in ECMAScript 5)
AttributeTypeDescription
Read-onlyBooleanReversed state of the ES5 [[Writable]] attribute.
DontEnumBooleanReversed state of the ES5 [[Enumerable]] attribute.
DontDeleteBooleanReversed state of the ES5 [[Configurable]] attribute.
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Accessor property

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Associates a key with one or two accessor functions (get and set) to retrieve or store a value and has the following attributes:

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
Attributes of an accessor property
AttributeTypeDescriptionDefault value
[[Get]]Function object or undefinedThe function is called with an empty argument list and retrieves the property value whenever a get access to the value is performed. See also get.undefined
[[Set]]Function object or undefinedThe function is called with an argument that contains the assigned value and is executed whenever a specified property is attempted to be changed. See also set.undefined
[[Enumerable]]BooleanIf true, the property will be enumerated in for...in loops.false
[[Configurable]]BooleanIf false, the property can't be deleted and can't be changed to a data property.false
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Note: Attribute is usually used by JavaScript engine, so you can't directly access it(see more about Object.defineProperty()).That's why the attribute is put in double square brackets instead of single.

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"Normal" objects, and functions

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A JavaScript object is a mapping between keys and values. Keys are strings (or {{jsxref("Symbol")}}s) and values can be anything. This makes objects a natural fit for hashmaps.

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Functions are regular objects with the additional capability of being callable.

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Dates

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When representing dates, the best choice is to use the built-in Date utility in JavaScript.

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Indexed collections: Arrays and typed Arrays

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Arrays are regular objects for which there is a particular relationship between integer-key-ed properties and the 'length' property. Additionally, arrays inherit from Array.prototype which provides to them a handful of convenient methods to manipulate arrays. For example, indexOf (searching a value in the array) or push (adding an element to the array), etc. This makes Arrays a perfect candidate to represent lists or sets.

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Typed Arrays are new to JavaScript with ECMAScript Edition 6 and present an array-like view of an underlying binary data buffer. The following table helps you to find the equivalent C data types:

+ +

{{page("/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray", "TypedArray_objects", "", 0, 3)}}

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Keyed collections: Maps, Sets, WeakMaps, WeakSets

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These data structures take object references as keys and are introduced in ECMAScript Edition 6. {{jsxref("Set")}} and {{jsxref("WeakSet")}} represent a set of objects, while {{jsxref("Map")}} and {{jsxref("WeakMap")}} associate a value to an object. The difference between Maps and WeakMaps is that in the former, object keys can be enumerated over. This allows garbage collection optimizations in the latter case.

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One could implement Maps and Sets in pure ECMAScript 5. However, since objects cannot be compared (in the sense of "less than" for instance), look-up performance would necessarily be linear. Native implementations of them (including WeakMaps) can have look-up performance that is approximately logarithmic to constant time.

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Usually, to bind data to a DOM node, one could set properties directly on the object or use data-* attributes. This has the downside that the data is available to any script running in the same context. Maps and WeakMaps make it easy to privately bind data to an object.

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Structured data: JSON

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JSON (JavaScript Object Notation) is a lightweight data-interchange format, derived from JavaScript but used by many programming languages. JSON builds universal data structures. See {{Glossary("JSON")}} and {{jsxref("JSON")}} for more details.

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More objects in the standard library

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JavaScript has a standard library of built-in objects. Please have a look at the reference to find out about more objects.

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З'ясування типу за допомогою оператора typeof

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The typeof operator can help you to find the type of your variable. Please read the reference page for more details and edge cases.

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Специфікації

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
СпецифікаціяСтатусКоментар
{{SpecName('ES1')}}{{Spec2('ES1')}}Первинне визначення.
{{SpecName('ES5.1', '#sec-8', 'Types')}}{{Spec2('ES5.1')}} 
{{SpecName('ES6', '#sec-ecmascript-data-types-and-values', 'ECMAScript Data Types and Values')}}{{Spec2('ES6')}} 
{{SpecName('ESDraft', '#sec-ecmascript-data-types-and-values', 'ECMAScript Data Types and Values')}}{{Spec2('ESDraft')}} 
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Див. також

+ + -- cgit v1.2.3-54-g00ecf