LayaBox---TypeScript---Symbols

Table of Contents

1. Introduction

2. Well-known Symbols

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1.Introduction

As of ECMAScript 2015, symbol is a new native type, just like number and string.

A value of type

symbol is created with the Symbol constructor.

let sym1 = Symbol();let sym2 = Symbol("key"); // optional string key

Symbols are immutable and unique.

let sym2 = Symbol("key");let sym3 = Symbol("key");sym2 === sym3; // false, symbols are unique

Like strings, symbols can also be used as keys for object properties.

let sym = Symbol();let obj = {[sym]: "value"};console.log(obj[sym]); // "value"

Symbols can also be combined with computed property name declarations to declare object properties and class members.

const getClassNameSymbol = Symbol();class C {[getClassNameSymbol](){return "C";}}let c = new C();let className = c[getClassNameSymbol](); // "C"

2. Well-known Symbols

The

Symbol.hasInstance method will be called by the instanceof operator.Constructor objects are used to identify whether an object is an instance of it.

Symbol.isConcatSpreadableBoolean value indicating that when Array.prototype.concat< is called on an object/span>, whether the array elements of this object can be expanded.

The

Symbol.iterator method is called by the for-of statement.Returns the default iterator for the object.

Symbol.match method, called by String.prototype.match.Regular expressions are used to match strings.

Symbol.replace method, called by String.prototype.replace, regular expressionThe formula is used to replace the matched substring in the string

Symbol.search method, called by String.prototype.search, regular expressionreturns the index of the matched part in the string.

Symbol.speciesThe function value, which is a constructor.Used to create derived objects.

Symbol.split method, called by String.prototype.split.Regular expressions are used to split strings.

The

Symbol.toPrimitive method, called by the ToPrimitive abstract operation, converts the object tothe corresponding raw value.

The

Symbol.toStringTag method is called by the built-in method Object.prototype.toString.Returns the default string description when the object is created.

Symbol.unscopables object, its own properties will be with scopeExcluded.