How to check if a component has a property definition programmatically in Angular?

Question

I have a property of a component in Angular that looks like this:

export class CarComponent implements OnInit {
  partNumber: number;

  checkIfItHasAPartNumberProperty() {
      return this.hasAProperty('partNumber');
  }

What is Angular equivalent for hasAProperty to check if this class contains a definition of a property by string name, eg. "partNumber"?

It is not a question about getting value of "partNumber", or checking directly if it has property "partNumber", but check programmatically if a component has a property of a given name (by string).

@Jota.Toledo hasOwnProperty does not seem to work for Angular component properties — Tom Smykowski
– Tom Smykowski, Commented Jun 27, 2019 at 12:22
See this post. The properties that have been initialized can be retrieved with hasOwnProperty but the others are not present in the class instance at runtime. You can see that with console.log(this). — Martin Parenteau
– Martin Parenteau, Commented Jun 27, 2019 at 13:18
@TomaszSmykowski - One answer suggests using custom transformers but I have never tried that. — Martin Parenteau
– Martin Parenteau, Commented Jul 3, 2019 at 15:51

ihor.eth · Accepted Answer · 2020-01-15 16:46:52Z

2

 const obj = this as object;
 obj.hasOwnProperty('prop')

Cast this to object and you should be able to call hasOwnProperty on it

EDIT This wont work on properties that haven't been initialized. For that case (if possible in your scenario) initialize the property with null and the above code will work

edited Jan 15, 2020 at 16:46

answered Jun 27, 2019 at 13:27

ihor.eth

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