使用带有打字稿的ES6符号

Question

我正在尝试运行这个简单的代码行 -

let FUNJECTOR_KEY = Symbol.for('funjector')

但我一直收到错误 - Cannot find name 'Symbol'. 我是打字稿的新手，所以我不确定是否需要包含一些内容？

在我的情况下，我不想使用这里解释的poly填充 - 在typescript中使用es-6符号

Answer 1

TypeScript编译器将TS转换为JS。 TSC在es5模式下找不到Symbol的声明。 所以你的错误纯粹是在编译时。 您不需要polyfill用于运行时。

要解决此问题，您可以将编译目标更改为es6 ，以便在标准库中定义Symbol 。 或者您可以手动添加定义（ 源 ）。

declare class Symbol {
    /** Returns a string representation of an object. */
    toString(): string;

    /** Returns the primitive value of the specified object. */
    valueOf(): Object;

    /**
      * Returns a new unique Symbol value.
      * @param  description Description of the new Symbol object.
      */
    constructor(description?: string);

    /**
    * Returns a Symbol object from the global symbol registry matching the given key if found.
    * Otherwise, returns a new symbol with this key.
    * @param key key to search for.
    */
    static for(key: string): Symbol;

    /**
      * Returns a key from the global symbol registry matching the given Symbol if found. 
      * Otherwise, returns a undefined.
      * @param sym Symbol to find the key for.
      */
    static keyFor(sym: Symbol): string;
}

// Well-known Symbols
declare module Symbol {
    /** 
      * A method that determines if a constructor object recognizes an object as one of the 
      * constructor’s instances.Called by the semantics of the instanceof operator. 
      */
    const hasInstance: Symbol;

    /** 
      * A Boolean value that if true indicates that an object should be flatten to its array 
      * elements by Array.prototype.concat.
      */
    const isConcatSpreadable: Symbol;

    /** 
      * A Boolean value that if true indicates that an object may be used as a regular expression. 
      */
    const isRegExp: Symbol;

    /** 
      * A method that returns the default iterator for an object.Called by the semantics of the 
      * for-of statement. 
      */
    const iterator: Symbol;

    /** 
      * A method that converts an object to a corresponding primitive value.Called by the 
      * ToPrimitive abstract operation. 
      */
    const toPrimitive: Symbol;

    /** 
      * A String value that is used in the creation of the default string description of an object.
      * Called by the built- in method Object.prototype.toString. 
      */
    const toStringTag: Symbol;

    /** 
      * An Object whose own property names are property names that are excluded from the with 
      * environment bindings of the associated objects.
      */
    const unscopables: Symbol;
}

警告：某些类型检查不适用于symbol 。 例如，您不能在接口上声明计算为符号的属性。