How Can I Handle Asynchronous Operations During Object Construction in JavaScript?

Can't use async/await in constructor: Workarounds for Asynchronous Object Construction

Problem: Attempting to utilize async/await syntax within a constructor function raises the error "Class constructor may not be an async method."

Cause: Async functions return promises, whereas constructors return the object being constructed. This creates a conflict, making it impossible to utilize both async/await and constructors simultaneously.

Workarounds:

1. Initialization Function (init()):

• Create an init() function within the class.
• The constructor calls init(), which allows asynchronous operations.

• Usage:

  var myObj = new myClass();
  myObj.init(function() {
    // Use myObj within the callback
  });

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• Implementation:

  class myClass {
    constructor () {
    }
    init (callback) {
        // Asynchronous operations and callback
    }
  }

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2. Builder Pattern:

• The constructor throws an error if called directly.
• A static build() method returns a promise for the object.

• Usage:

  myClass.build().then(function(myObj) {
    // Use myObj
  });
  
  async function foo () {
    var myObj = await myClass.build();
  }

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• Implementation:

  class myClass {
    constructor (async_param) {
        if (async_param === undefined) {
            throw new Error('Cannot be called directly');
        }
    }
    static build () {
        return doSomeAsyncStuff()
               .then(function(async_result){
                   return new myClass(async_result);
               });
    }
    // Async/await equivalent:
    static async build () {
        var async_result = await doSomeAsyncStuff();
        return new myClass(async_result);
    }
  }

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Note: Builders can use callbacks instead of promises.

Calling Functions within Static Functions:

• Static functions are not bound to objects (unlike instance methods).
• Therefore, this refers to the class, not the instantiated object.

• To call instance methods from static functions, make them either regular functions or static methods.

  class A {
    static foo () {
        bar1();   // OK
        A.bar2(); // OK
    }
    static bar2 () {}
  }
  function bar1 () {}

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