Unexpected token. A constructor, method Error in TS [Fixed]

# Unexpected token. A constructor, method Error in TS

The "Unexpected token. A constructor, method, accessor, or property was expected" error occurs when we use the var or let keywords to declare a class property or the function keyword in a class.

To solve the error, remove the var, let and function keywords from your class.

Here are 2 examples of how the error occurs.

index.ts

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class A {
  // ⛔️ Error (using var, let)
  var a: number = 100;
  let b: string = 'hello';

  // ⛔️ Error: Unexpected token. A constructor,
  // method, accessor, or property was expected.ts(1068)
  function myFunction() {

  }
}

unexpected token a constructor method accessor or property

We used the var and let keywords to assign properties to the class and the function keyword to declare class method.

To resolve the issue, remove the var, let and function keywords from your class.

index.ts

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class A {
  a = 100;
  b = 'bobbyhadz.com';

  myFunction() {
    console.log(this.a);
  }
}

const myInstance = new A();

console.log(myInstance.a); // 👉️ 100
console.log(myInstance.b); // 👉️ "bobbyhadz.com"

myInstance.myFunction(); // 👉️ 100

remove var let function keyword from class

The code for this article is available on GitHub

The class has 2 propertied - a and b and a method named myFunction.

# Taking arguments via the constructor method

You will often have to take arguments when creating class instances. You can do that via the constructor method.

index.ts

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class A {
  constructor(
    public a: number,
    public b: string,
  ) {
    this.a = a;
    this.b = b;
  }

  myFunction() {
    console.log(this.a);
  }
}

const myInstance = new A(42, 'bobbyhadz.com');

console.log(myInstance.a); // 👉️ 42
console.log(myInstance.b); // 👉️ "bobbyhadz.com"

taking arguments via constructor method

The code for this article is available on GitHub

Notice that we assigned the a and b properties inside the constructor method and we aren't using the var, let or function keywords anywhere inside the class.

The class in the example is a more concise version of the following class.

index.ts

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class A {
  a: number;
  b: string;

  constructor(a: number, b: string) {
    this.a = a;
    this.b = b;
  }

  myFunction() {
    console.log(this.a);
  }
}

const myInstance = new A(42, 'bobbyhadz.com');

console.log(myInstance.a); // 👉️ 42
console.log(myInstance.b); // 👉️ "bobbyhadz.com"

We had to type the a and b class properties twice to achieve the same result.

The previous example with the explicit use of the public keyword in the constructor is more widely used.

# Using default values for constructor parameters

You can also use default values for constructor parameters.

index.ts

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class A {
  constructor(
    public a = 100,
    public b = 'bobbyhadz.com',
  ) {
    this.a = a;
    this.b = b;
  }

  myFunction() {
    console.log(this.a);
  }
}

const myInstance = new A();

console.log(myInstance.a); // 👉️ 100
console.log(myInstance.b); // 👉️ "bobbyhadz.com"

using default values for constructor parameters

The code for this article is available on GitHub

We created an instance of the class without passing any parameters to the constructor function, so the a and b properties are set to the default values.

# Using arrow functions for class methods

You can also use arrow functions for class methods.

index.ts

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class A {
  constructor(
    public a = 100,
    public b = 'bobbyhadz.com',
  ) {
    this.a = a;
    this.b = b;
  }

  myFunction = () => {
    console.log(this.a);
  };
}

const myInstance = new A();

console.log(myInstance.a); // 👉️ 100
console.log(myInstance.b); // 👉️ "bobbyhadz.com"

myInstance.myFunction(); // 👉️ 100

The code for this article is available on GitHub

Notice that we aren't using the const, let or var keywords in the method's definition.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

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Unexpected token. A constructor, method Error in TS [Fixed]