运算符“+”不能应用于 TypeScript 中的“String”和“String”类型
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Operator '+' cannot be applied to types 'String' and 'String' in TypeScript
提问by Engr. Hasanuzzaman Sumon
I am new to TypeScript trying to play with it. But I face a wired problem. When I try to concatenate two Stringtype using +operator it's give an error that is
我是 TypeScript 的新手，正在尝试使用它。但我面临一个有线问题。当我尝试String使用+运算符连接两种类型时，它给出了一个错误
Operator '+' cannot be applied to types 'String' and 'String'
运算符 '+' 不能应用于类型 'String' 和 'String'
My Code snap is
我的代码快照是
var firstName: String = 'Foo';
var lastName: String = 'Bar';
var name = firstName + lastName;
If I use stringinstead Stringor add extra ''it works fine. I checked, within JavaScript we can use +on two Stringobject then why it's show error in TypeScript ? Is it bug or feature ? I definitely missing something. Detail explanation appreciated.
如果我string改用 String或添加额外的''它工作正常。我检查过，在 JavaScript 中我们可以+在两个String对象上使用，那么为什么它在 TypeScript 中显示错误？它是错误还是功能？我肯定错过了一些东西。详细解释表示赞赏。
回答by Ryan Cavanaugh
Stringis not the same as string. Always use stringunless you really, really know what you're up to.
String不一样string。string除非您真的非常清楚自己在做什么，否则请始终使用。
The upper-case name Stringrefers to the boxed version of a primitive string. These should generally be avoided wherever possible -- they don't behave like normal strings in subtle and unexpected ways (for example typeof new String('hello')is "object", not "string").
大写名称String指的是原始字符串的装箱版本。这些通常应该尽可能避免——它们不会以string微妙和意外的方式表现得像普通s（例如typeof new String('hello')is "object"， not "string"）。
