CODEWITHSUNDEEP
javascriptnode.jstypescript
Narayanan
Narayanan

Reputation: 207

Define Callback in interface Typescript

I want to implement an interface with a list of functions and attributes, few functions required to work on callback mode. For example

interface Writer{
     readData : (fileLocation: string) => void;
     generatData: (fileLocation: string) => void;
}

I would like to execute generateData function and notify after job is done. For example

const WriterInstance:Writer ={
   generateData("C:/workspace" , ()=>{
       console.log("work is done");
   });
   readData("C:/workspace/file1.text" , ()=>{
       console.log("work is done");
   })
}

I am totally misunderstanding the syntax & invocation of callbacks in the interface. If anyone explains with example then it will be great.

Upvotes: 2

Views: 3068

Answers (3)

Syder
Syder

Reputation: 372

// Define writer interface
interface Writer{
     readData : (fileLocation: string, callback: () => void) => void;
     generateData: (fileLocation: string, callback: () => void) => void;
}

// Create writer
const writerInstance: Writer = {
   generateData: (fileLocation: string, callback: () => void) => {
    // generate data
    callback();
},
   readData: (fileLocation: string, callback: () => void) => {
    //read data
    callback();
}
}

// Call writer methods
writerInstance.generateData("C:/workspace", ()=>{
     console.log("work is done");
 });

writerInstance.readData("C:/workspace/file1.text" , ()=>{
     console.log("work is done");
 });

Upvotes: 1

hoangdv
hoangdv

Reputation: 16147

Just imagine that the callback function is a normal parameter. Then, define WriterInstance as a normal object - Just define it's properties

interface Writer{
  readData : (fileLocation: string, callback: () => void) => void;
  generateData: (fileLocation: string, callback: (error: Error, data?: any) => void) => void;
}

const WriterInstance: Writer = {
  readData: (fileLocation: string, callback: () => void) => {
    // dome something with fileLocation
    callback();
  },

  generateData: (fileLocation: string, callback: (error: Error, data?: any) => void) => {
    // dome something with fileLocation
    callback(null, true);
  }
}

// usage of WriterInstance
WriterInstance.generateData('C:/workspace/file1.text', (error, data) => {
  if (error) {
    console.log('work is not done');
    return console.log(error);
  }
  console.log('work is done');
});

Upvotes: 2

captain hak
captain hak

Reputation: 912

In your interface, you want to represent a function with two parameters, the first one is a string and the second one is a function so you can write it like that:

interface Writer{
     readData : (fileLocation: string, callback: ()=>void) => void;
     generateData: (fileLocation: string, callback: ()=>void) => void;
}

Upvotes: 1

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