Typescript - inline class without dynamically added properties
I have a set of typescript objects that have been triggered, but in code I need to dynamically add some properties to this object. If I need to serialize an object by specifying it - how can I do that so that it doesn't include dynamically added properties? Since I have many classes and inner classes, I am looking for a general approach rather than one by one.
So, as an example, I have a class defined like this:
export class Car {
public colour: string = '';
public model: string = '';
public diesel?: boolean = false;
constructor () {}
}
Now in code, I am setting the above car as the one I am currently driving:
let car: Car = new Car();
car.model = 'modelA';
car.colour = 'black';
car['active'] = true;
And then somewhere in the code I need to take the active car and serialize the object so that I can send the data to the server:
JSON.stringify({'data': car});
What I'm looking for is now a string representation of an object with no dynamically added properties, but the approach is generic so I don't need to describe what I want to remove.
All help is needed; -)
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You can keep a list of "known keys" and use them in serialization:
class Car {
private static keys = ["colour", "model", "diesel"];
public colour: string = '';
public model: string = '';
public diesel?: boolean = false;
constructor() { }
toJsonString(): string {
const data = {};
Car.keys.forEach(key => data[key] = this[key]);
return JSON.stringify(data);
}
}
You can use decorators to create this static list.
Or:
class Car {
public colour: string = '';
public model: string = '';
public diesel?: boolean = false;
constructor() {
this.toJsonString = function (keys) {
const data = {};
keys.forEach(key => data[key] = this[key]);
return JSON.stringify(data);
}.bind(this, Object.keys(this));
}
toJsonString: () => string;
}
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You can create a car and it will only have normal properties. Then flip all its properties and copy the value from another car:
let car: Car = new Car();
car.model = 'modelA';
car.colour = 'black';
car['active'] = true;
let withoutDynamics = new Car();
for (let prop in withoutDynamics) {
// Check for hasOwnProperty if you like, depending on whether you
// properties from the prototype
withoutDynamics[prop] = car[prop];
}
JSON.stringify({'data': withoutDynamics });
You can include this in a generic function to be used with other classes (if they have a constructor that takes no parameters):
function noDynamics<T>(type: { new (): T; }, withDynamics: T): T {
let withoutDynamics = new type();
for (let prop in withoutDynamics) {
withoutDynamics[prop] = withDynamics[prop];
}
return withoutDynamics;
}
JSON.stringify({'data': noDynamics(Car, car) });
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You can store an array of original keys in a property and use a custom toJSON
implementation in your class to control that only the original keys are serialized:
export class Car {
public colour: string = '';
public model: string = '';
public diesel?: boolean = false;
private _keys: string[] // Note that this is not initialized
constructor() {
this._keys = Object.keys(this);
}
toJSON() {
var obj: any = {};
this._keys.forEach(key => {
obj[key] = this[key]
});
return obj
}
}
let car: Car = new Car();
car.model = 'modelA';
car.colour = 'black';
car['active'] = true;
console.log(JSON.stringify({ 'data': car }));
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