How to validate the number of arguments in TypeScript

Question

I (only) use arguments to throw an error when an invalid number of arguments are passed to a function.

const myFunction = (foo) => {
  if (arguments.length !== 1) {
     throw new Error('myFunction expects 1 argument');
  }
}

Unfortunately in TypeScript I get the error The 'arguments' object cannot be referenced in an arrow function in ES3 and ES5. Consider using a standard function expression. when referenced in arrow function.

How can I (always) validate the number of arguments in TypeScript?

Possible duplicate of Official information on `arguments` in ES6 Arrow functions? — pushkin
– pushkin, Commented Jan 9, 2019 at 21:01

Matt H · Accepted Answer · 2019-01-09 20:47:49Z

2

The code snippet that you posted doesn't seem to have the same error for me. I do see that error if I change it to be an arrow function:

const myFunction = (foo) => {
    if (arguments.length !== 1) {
        throw new Error('myFunction expects 1 argument');
    }
}

You can try doing something like:

const myFunction = (...foo) => {
    if (foo.length !== 1) {
        throw new Error('myFunction expects 1 argument');
    }
}

To work around the issue.

answered Jan 9, 2019 at 20:47

Matt H

1,9911 gold badge9 silver badges8 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Karol Majewski · Accepted Answer · 2019-01-09 23:14:58Z

2

You can also enforce the arity of your function in compile-time:

const myFunction = (...args: [any]) => {
  /* ... */
}

myFunction(1);    // OK
myFunction(1, 2); // Compile-time error

answered Jan 9, 2019 at 23:14

Karol Majewski

26.2k9 gold badges53 silver badges57 bronze badges

Collectives™ on Stack Overflow

How to validate the number of arguments in TypeScript

2 Answers 2

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related