[英]when are typescript/js decorators executed
When do decorators get executed? 装饰器何时被执行?
class Person {
@SomeDecorator
age
}
What about static properties? 静态属性怎么样?
A property decorator executes early - when the class is defined. 属性装饰器早期执行 - 定义类时。 You don't need to construct an instance, or access the property.
您无需构造实例或访问该属性。
Example: this logs age
without the Person
class even being constructed. 示例:这会记录
age
而不会构造Person
类。 The same applies if the property is static. 如果属性是静态的,则同样适用。
function SomeDecorator(a, b) {
console.log(b);
}
class Person {
@SomeDecorator
public age: number;
}
If you are after hooking into the get and set actions on the property - that is possible too. 如果您正在追踪物业的获取和设定行动 - 这也是可能的。 Here is an example from a listing in Pro TypeScript (Second Edition) .
以下是Pro TypeScript(第二版)中的列表示例。 It works by wrapping the getter and setter.
它通过包装getter和setter来工作。
function log(target: any, key: string) {
let value = target[key];
// Replacement getter
const getter = function () {
console.log(`Getter for ${key} returned ${value}`);
return value;
};
// Replacement setter
const setter = function (newVal) {
console.log(`Set ${key} to ${newVal}`);
value = newVal;
};
// Replace the property
if (delete this[key]) {
Object.defineProperty(target, key, {
get: getter,
set: setter,
enumerable: true,
configurable: true
});
}
}
class Calculator {
@log
public num: number;
square() {
return this.num * this.num;
}
}
console.log('Construct');
const calc = new Calculator();
console.log('Set');
// Set num to 4
calc.num = 4;
console.log('Get');
// Getter for num returned 4
// Getter for num returned 4
calc.square();
The output of this listing is: 此列表的输出是:
Construct (manual log)
Set (manual log)
-> Set num to 4
Get (manual log)
-> Getter for num returned 4
-> Getter for num returned 4
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