typescript 如何修复错误 TS1015：参数不能有问号和初始值设定项？
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How do I fix error TS1015: Parameter cannot have question mark and initializer?
提问by
I have just upgraded to TypeScript beta 0.9 and now I'm getting the error:
我刚刚升级到 TypeScript beta 0.9，现在出现错误：
TS1015: Parameter cannot have question mark and initializer
TS1015：参数不能有问号和初始值设定项
This was valid before, how do I fix this?
这以前是有效的，我该如何解决这个问题？
Here's an example of the code that's generating this error:
这是生成此错误的代码示例：
functionName(parameterName?: typeName = defaultValue): typeName
回答by
If you look in the TypeScript Language Specificationdocument you can find a wealth of detail about the language syntax.
如果您查看TypeScript 语言规范文档，您可以找到有关语言语法的大量详细信息。
Section 3.9.2describes call signatures i.e. the syntax used to call functions and constructors etc.
第3.9.2节描述了调用签名，即用于调用函数和构造函数等的语法。
Section 3.9.2.2is specifically about the parameters associated with a call.
第3.9.2.2节专门介绍与调用相关的参数。
It defines optional parameters as:
它将可选参数定义为：
AccessibilityModifieropt?BindingIdentifierOrPattern???TypeAnnotationopt
AccessibilityModifieropt?BindingIdentifierOrPattern?TypeAnnotationopt?Initializer
AccessibilityModifieropt?BindingIdentifierOrPattern???TypeAnnotationopt
AccessibilityModifieropt?BindingIdentifierOrPattern?TypeAnnotationopt?Initializer
We can see see that either using '?' ORproviding a default value Initializerwill mark the parameter as being optional.
我们可以看到，要么使用'?' OR提供默认值Initializer会将参数标记为可选。
So to fix the compiler error you can simply remove the '?' and leave the default value and it will remain as an optional parameter as you intend.
因此，要修复编译器错误，您可以简单地删除“？” 并保留默认值，它将按照您的意愿保留为可选参数。
