CODEWITHSUNDEEP
classtypescriptecmascript-6
user8116198
user8116198

Reputation:

Typescript | Call a function every time a function is called

I am trying to write a Typescript API service. For the service I need a way to check that the method exists when a function such as get is called.

I realise I can do like 

get(endpoint: string) {
    this.handleRequest();
}

post(endpoint: string, data: any) {
    this.handleRequest();
}

But I don't particularly want to do that are the top of every method so I didn't know if there was a way to listen within the constructor of the Typescript class for a call of a child function.

It seems a little far fetched to be able to do this but it would be extremely useful in cases like mine so I don't have to keep on doing it.

export class ApiService {
    base_url: string = 'https://jsonplaceholder.typicode.com/posts';
    methods = ['GET', 'POST', 'PUT', 'PATCH', 'DELETE'];

    /**
     * Create an instance of ApiService.
     * @param {string} base_url
     */
    constructor(base_url: string = null) {
        this.base_url = base_url ? base_url : this.base_url;
    }

    get(endpoint: string): string {
        // duplicated line
        this.handleRequest();

        return 'get method';
    }

    post(endpoint: string, data: any): string {
        // duplicated line
        this.handleRequest();

        return 'post method';
    }

    protected handleRequest(): string {
        return 'handle the request';
    }
}

Upvotes: 2

Views: 2947

Answers (1)

Titian Cernicova-Dragomir
Titian Cernicova-Dragomir

Reputation: 249586

You can do this using a decorator that will override all methods of the class with a method that calls the original implementation and your extra method:

function handleRequest() {
    return function<TFunction extends Function>(target: TFunction){
        for(let prop of Object.getOwnPropertyNames(target.prototype)){
            if (prop === 'handleRequest') continue;
            // Save the original function 
            let oldFunc: Function = target.prototype[prop];
            if(oldFunc instanceof Function) {
                target.prototype[prop] = function(){
                    this['handleRequest'](); // call the extra method
                    return oldFunc.apply(this, arguments); // call the original and return any result
                }
            }
        }
    }
}

@handleRequest()
export class ApiService {
    base_url: string = 'https://jsonplaceholder.typicode.com/posts';
    methods = ['GET', 'POST', 'PUT', 'PATCH', 'DELETE'];

    /**
     * Create an instance of ApiService.
     * @param {string} base_url
     */
    constructor(base_url: string = null) {
        this.base_url = base_url ? base_url : this.base_url;
    }

    get(endpoint: string): string {
        return 'get method';
    }

    post(endpoint: string, data: any): string {
        return 'post method';
    }

    protected handleRequest(): void {
        console.log('handle the request');
    }
}

let s = new ApiService();
s.get("");
s.post("", null);

Upvotes: 6

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