typeof param[key] typescript
时间: 2024-01-05 20:03:26 浏览: 33
This code snippet is checking the type of a value stored in an object's property. It is written in TypeScript, a typed superset of JavaScript.
Assuming "param" is an object and "key" is a string representing one of its property names, the code is accessing that property with bracket notation (i.e. param[key]).
The "typeof" keyword is then used to get the type of the value stored in that property. This will return a string representing the type, such as "string", "number", "boolean", etc.
For example, if "param" has a property called "age" with a value of 25, and "key" is the string "age", then typeof param[key] would return "number".
相关问题
typescript typeof
The `typeof` keyword in TypeScript is used to get the type of a value or a variable at runtime. It is similar to the `typeof` operator in JavaScript, but with added support for type annotations and type inference.
For example, consider the following code:
```typescript
const x = 42;
const y = "hello";
console.log(typeof x); // "number"
console.log(typeof y); // "string"
```
Here, the `typeof` operator is used to get the types of the variables `x` and `y` at runtime.
In TypeScript, `typeof` can also be used with type annotations and type inference to create more type-safe code. For example:
```typescript
function getLength(str: string) {
return str.length;
}
const message = "hello";
const length = getLength(message);
console.log(length); // 5
console.log(typeof length); // "number"
```
Here, the `getLength` function takes a string parameter and returns its length. The `typeof` keyword is used to infer the type of the `length` variable, which is `number`. This ensures that we don't accidentally try to use `length` as a string or some other type later on in our code.
typeof 宇keyof
在TypeScript中,typeof操作符用于获取一个变量或表达式的类型。它返回一个代表该类型的值。相比之下,keyof操作符则用于获取一个类型的所有属性名的联合类型。它返回一个包含了类型中所有属性名的联合类型。<span class="em">1</span><span class="em">2</span><span class="em">3</span>
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