CODEWITHSUNDEEP
javascriptecmascript-6
Shaharyar
Shaharyar

Reputation: 12449

ES6 object destructuring mandatory parameters

Here is the function, password is mandatory but other id and name have default values:

function name({id = null, name = 'user', password}) { }

Results:

name();     //throws error as expected
name({});   //passes 'password' as 'undefined' - should've thrown error

How can I make this function throw an error if password is not provided using ES6 functionality?

Upvotes: 1

Views: 817

Answers (4)

Ori Drori
Ori Drori

Reputation: 192006

Note: This is an ugly hack using the default parameters, and I prefer @Scimonster's answer.

You can actually run a function, and even an IIFE as a default param. The IIFE can throw an error:

function name({
  id = null, 
  name = 'user',
  password = (() => { throw new Error('password not defined'); })()
}) { 
  console.log(id, name, password);
}
  
name({ id: 1, name: 'the name', password: 'the password' }); // works

name({}); // throws an error

Upvotes: 2

T.J. Crowder
T.J. Crowder

Reputation: 1074555

Scimonster's answer is spot-on about what the probelm is.

If you like, you can handle it a bit more declaratively by using a utility function to throw an Error in the function parameter list:

// Utility function:
function throwRequired(name) {
  throw new Error(`'${name}' is required`);
}

function name({id = null, name = 'user', password = throwRequired("password")}) {
  console.log("All is good, password is: " + password);
}

try {
  name();     //throws error as expected
} catch (e) {
  console.log("Got error from name():", e.message);
}
try {
  name({});     //throws error as expected
} catch (e) {
  console.log("Got error from name({}):", e.message);
}
name({password: "foo"}); // works

That works because the initializer on a default parameter is only evaluated if it's required to fill in the default.

Upvotes: 2

Nina Scholz
Nina Scholz

Reputation: 386654

You could assign the same variable, it throws an error Use before declaration, if not given. 

function name({ id = null, name = 'user', password = password }) {
    console.log(password);
}
name({});

If set, then it works without error.

function name({ id = null, name = 'user', password = password }) {
    console.log(password);
}
name({ password: 'foo' });

Upvotes: 4

Scimonster
Scimonster

Reputation: 33409

You didn't make it required, you simply didn't provide a default value.

function name({id = null, name = 'user', password}) {
     if (password == undefined) {
        throw new Error('password is required');
    }

The reason it threw an error the first time is because it tried to destructure undefined, which is impossible.

Upvotes: 2

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