Guide on waiting for an asynchronous function in the constructor in JavaScript

Question

Guide on waiting for an asynchronous function in the constructor in JavaScript

In the process of creating a JS class, I encounter a situation where I need to call wasmFunc in the constructor and store its output in this.val. However, since wasmFunc comes from a WebAssembly file, it is necessary to execute an async function called loadWasm before wasmFunc becomes callable. The code snippet below demonstrates my attempt:

// index.js
async loadWasm() {
   // load wasm file
}

export class MyClass {
  constructor() {
    await loadWasm(); // This operation will not work
    this.val = wasmFunc();
  }
}

export const myObj = new MyClass();

My goal is for the exported file index.js to offer a ready-to-use myObj. Unfortunately, using await within the constructor is prohibited.

Do you have any solutions or thoughts on how to address this challenge?

javascript async-await webassembly

Answer 1

Answer №1

Constructors are required to return an instance of the class being constructed
Asynchronous functions need to return a promise

Due to the fact that a function can only perform one task, it is not possible for a constructor function to be asynchronous.

Utilizing a Helper Function

A helper function can be used:

// index.js
async loadWasm() {
   // load wasm file
}

export class MyClass {
  constructor(wasm) {
    this.val = wasm;
  }
}

async function myClassFactory() {
    const wasm = await loadWasm();
    const instance = new MyClass(wasm);
    return instance;
}

You will need to await the result obtained from calling myClassFactory().

Storing a Promise in the Object

An alternative approach is to store a promise within the object created:

// index.js
async loadWasm() {
   // load wasm file
}

export class MyClass {
  constructor() {
    const wasmPromise = loadWasm();
    this.val = wasmPromise;
  }

  async doSomethingWithValue() {
    const wasm = await this.val;
    console.log(wasm);
  }
}

Answer 2

Constructors are required to return an instance of the class being constructed
Asynchronous functions need to return a promise

Due to the fact that a function can only perform one task, it is not possible for a constructor function to be asynchronous.

Utilizing a Helper Function

A helper function can be used:

// index.js
async loadWasm() {
   // load wasm file
}

export class MyClass {
  constructor(wasm) {
    this.val = wasm;
  }
}

async function myClassFactory() {
    const wasm = await loadWasm();
    const instance = new MyClass(wasm);
    return instance;
}

You will need to await the result obtained from calling myClassFactory().

Storing a Promise in the Object

An alternative approach is to store a promise within the object created:

// index.js
async loadWasm() {
   // load wasm file
}

export class MyClass {
  constructor() {
    const wasmPromise = loadWasm();
    this.val = wasmPromise;
  }

  async doSomethingWithValue() {
    const wasm = await this.val;
    console.log(wasm);
  }
}

Answer 3

Answer №2

class MyNewClass {
    async constructor() {

    }
}

-> Uncaught SyntaxError: Class constructor may not be an async method

Edit: However, there is a workaround.

class MyNewClass {
    constructor(args) {
        this.arguments = args;
    };
    static async create(...args) {
        return new this(args);
    }
}
-> MyNewClass.create("test")

Answer 4

class MyNewClass {
    async constructor() {

    }
}

-> Uncaught SyntaxError: Class constructor may not be an async method

Edit: However, there is a workaround.

class MyNewClass {
    constructor(args) {
        this.arguments = args;
    };
    static async create(...args) {
        return new this(args);
    }
}
-> MyNewClass.create("test")

Answer 5

Answer №3

class CustomClass {
    async loadWebAssembly() {

    }

    async executeFunction(){
        await this.loadWebAssembly(); // This won't work
        this.value = wasmFunction();
    }

  constructor() {
    this.executeFunction()
  }
}

export const customObject = new CustomClass();

Give this a shot. It's worth a try.

Answer 6

class CustomClass {
    async loadWebAssembly() {

    }

    async executeFunction(){
        await this.loadWebAssembly(); // This won't work
        this.value = wasmFunction();
    }

  constructor() {
    this.executeFunction()
  }
}

export const customObject = new CustomClass();

Give this a shot. It's worth a try.

Guide on waiting for an asynchronous function in the constructor in JavaScript

Answer №1

Utilizing a Helper Function

Storing a Promise in the Object

Answer №2

Answer №3

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