Creating property inside constructor with Typescript

Question

I have a javascript code that works perfectly:

class myController {
   constructor () {
      this.language = 'english'
   }
}

BUT when I try to do the same with Typescript

export default class myController {
  constructor () {
    this.language = 'english'
  }
}

It gives me the following error:

Property 'language' does not exist on type 'myController'.ts(2339)

Why exactly this happen when trying to create a property for myController?
What would be the right way to do so?

You need to declare a variable out of the constructor like private language: string. — Vagner Wentz
– Vagner Wentz, Commented Aug 19, 2021 at 13:10

AleksW · Accepted Answer · 2021-08-19 13:11:10Z

5

Because you are trying to set a property which does not exist in the class as it says, declare it somewhere in the class before you try set it, i.e:

export default class myController {
  private language: string;
  constructor () {
    this.language = 'english'
  }
}

answered Aug 19, 2021 at 13:11

AleksW

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3 Comments

Vagner Wentz Over a year ago

I maked the same response but I add a comment hahaha

PlayHardGoPro Over a year ago

Thanks guys. I'll upvote both. I thought as this could be done with javascript I would also be able to do it in TS. Thanks

jcalz Over a year ago

"I thought as this could be done with javascript I would also be able to do it in TS" See stackoverflow.com/questions/41750390/…

Thomas Smith · Accepted Answer · 2021-08-19 17:37:31Z

3

It needs to be declared as a Property on the type (typically before the constructor):

export default class myController {
  language: string;
  constructor () {
    this.language = 'english'
  }
}

edited Aug 19, 2021 at 17:37

answered Aug 19, 2021 at 13:13

Thomas Smith

311 silver badge4 bronze badges

2 Comments

Thomas Smith Over a year ago

See typescriptlang.org/docs/handbook/2/classes.html for more info

AleksW Over a year ago

Just as a tip: It does not need to be above the constructor, all property declarations are called before the constructor no matter where in the class they are, having them above does make the most sense though

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