CODEWITHSUNDEEP
es6-class
Panu Logic
Panu Logic

Reputation: 2263

How to detect if JavaScript (ES6) class has a non-default constructor?

I would like to know by some form of reflection or other means if a given ES6 class has a user-written non-default constructor, or not.

Upvotes: 2

Views: 128

Answers (2)

zerkms
zerkms

Reputation: 254916

You can invoke the Classname.prototype.constructor.toString() (where Classname is the inspected class name) and get the source string for the class. Which you can then parse and see if it was a constructor declared or not.

Presumably, you need a decent parser for that, but it's another story.

References:

Upvotes: 1

Trash Can
Trash Can

Reputation: 6814

Assuming that user-provided constructor has one argument or more, you can do that by checking the length property of the function(class). But if the constructor takes no argument, there is simply no way as far as I know

function Person(fName, lName) {
    this.firstName = fName;
    this.lastName = lName
}
console.log(Person.length);

function Person2() {}
console.log(Person2.length);

class Person3 {
    constructor(f,l) {}
}
console.log(Person3.length);

class Person4 {
}
console.log(Person4.length);

Upvotes: 1

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