TypeScript 或 JavaScript 类型转换
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TypeScript or JavaScript type casting
提问by Klaus Nji
How does one handle type casting in TypeScript or Javascript?
如何处理 TypeScript 或 Javascript 中的类型转换？
Say I have the following TypeScript code:
假设我有以下 TypeScript 代码：
module Symbology {
export class SymbolFactory {
createStyle( symbolInfo : SymbolInfo) : any {
if (symbolInfo == null)
{
return null;
}
if (symbolInfo.symbolShapeType === "marker") {
// how to cast to MarkerSymbolInfo
return this.createMarkerStyle((MarkerSymbolInfo) symbolInfo);
}
}
createMarkerStyle(markerSymbol : MarkerSymbolInfo ): any {
throw "createMarkerStyle not implemented";
}
}
}
where SymbolInfois a base class. How do I handle typecasting from SymbolInfoto MarkerSymbolInfoin TypeScript or Javascript?
哪里SymbolInfo是基类。如何在 TypeScript 或 Javascript 中处理从SymbolInfoto 的类型转换MarkerSymbolInfo？
回答by blorkfish
You can cast like this:
你可以这样投射：
return this.createMarkerStyle(<MarkerSymbolInfo> symbolInfo);
Or like this if you want to be compatible with tsx mode:
或者像这样，如果你想与 tsx 模式兼容：
return this.createMarkerStyle(symbolInfo as MarkerSymbolInfo);
Just remember that this is a compile-time cast, and not a runtime cast.
请记住，这是一个编译时强制转换，而不是运行时强制转换。
回答by Alex
This is called type assertionin TypeScript, and since TypeScript 1.6, there are two ways to express this:
这在 TypeScript 中称为类型断言，从 TypeScript 1.6 开始，有两种表达方式：
// Original syntax
var markerSymbolInfo = <MarkerSymbolInfo> symbolInfo;
// Newer additional syntax
var markerSymbolInfo = symbolInfo as MarkerSymbolInfo;
Both alternatives are functionally identical. The reason for introducing the as-syntax is that the original syntax conflicted with JSX, see the design discussion here.
这两种选择在功能上是相同的。引入as-syntax的原因是原始语法与JSX冲突，请参阅此处的设计讨论。
If you are in a position to choose, just use the syntax that you feel more comfortable with. I personally prefer the as-syntax as it feels more fluent to read and write.
如果您可以选择，请使用您觉得更舒服的语法。我个人更喜欢as-syntax，因为它读起来更流畅。
