typescript 如何清除打字稿中的类型化数组并保留其类型？
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How to clear a typed array in typescript and preserving its type?
提问by Vincent-cm
Now in a class, I declared an array with type: CustomType, like below
现在在一个类中，我声明了一个类型为：CustomType 的数组，如下所示
class Example {
public exampleArray: CustomType[];
public clearArray() {
this.exampleArray = [];
}
}
As you can see the clearArray assign an UNDEFINED type of an empty array, which seems lost the type information.
如您所见， clearArray 分配了一个空数组的 UNDEFINED 类型，这似乎丢失了类型信息。
How I can clear the array but preserving its declared type?
如何清除数组但保留其声明的类型？
回答by Titian Cernicova-Dragomir
The type information is determined by the type annotation on the field (exampleArray: CustomType[]). At runtime Javascript arrays are untyped anyway. The compiler will allow an empty array ([]) to be assigned to anything as this is considered safe, since there are no objects inside, it can be an array of CustomType. The field type will then prevent you form pushing to the array objects of any other type:
类型信息由字段 ( exampleArray: CustomType[])上的类型注释确定。在运行时 Javascript 数组无论如何都是无类型的。编译器将允许将空数组 ( []) 分配给任何东西，因为这被认为是安全的，因为内部没有对象，它可以是CustomType. 然后字段类型将阻止您将表单推送到任何其他类型的数组对象：
class CustomType { x: number}
class Example {
public exampleArray: CustomType[];
public clearArray() {
this.exampleArray = [];
this.exampleArray.push(new CustomType())
this.exampleArray.push({}) // error not a `CustomType`
}
}
Note
笔记
If this had been a variable with no type annotation, the variable would have been inferred to any[], which can lead to problems (types are not checked on either when assigning an array literal or when you would push to the array):
如果这是一个没有类型注释的变量，则该变量将被推断为any[]，这可能会导致问题（在分配数组文字或推送到数组时不会检查类型）：
let noAnnotationArray = [] // any[]
In this case, adding a type annotation is still the best way to go. Type assertions (as suggested in other answers) can lead to uncaught errors if later someone adds an item to the array:
在这种情况下，添加类型注释仍然是最好的方法。如果稍后有人将项目添加到数组中，则类型断言（如其他答案中所建议的）可能会导致未捕获的错误：
let withAnnotation:CustomType[] = [{}] // error
let withAssertion = <CustomType[]>[{}] // no error even though we assign {}
回答by Luke Becker
This post seems to be out of date. There is a new way to do this.
这个帖子似乎已经过时了。有一种新方法可以做到这一点。
this.array = [] as CustomType[];
回答by jms
You could try with
你可以试试
this.exampleArray = <CustomType[]>[];
回答by Sarthak Aggarwal
There can be 3 ways of emptying an array
清空数组有3种方式
setting its length = 0
myArr.length = 0;using splicemethod Array
myArr.splice(0,myArr.length);Pop() each element of array
while(myArr.length){ myArr.pop(); }
设置其长度 = 0
myArr.length = 0;使用拼接方法数组
myArr.splice(0,myArr.length);Pop() 数组的每个元素
while(myArr.length){ myArr.pop(); }
回答by Punith Mithra
You can always clear the list items by changing the length property to 0
您始终可以通过将 length 属性更改为 0 来清除列表项
eg: this.exampleArray.length = 0
例如： this.exampleArray.length = 0
Setting length to 0 clears all the elements in the array without altering the reference of the array.
将 length 设置为 0 会清除数组中的所有元素而不更改数组的引用。
