How to update linklabels of selectedlink?

   const linkTextValidation = ((textblock, oldstr, newstr) => {
 
      this.dia.model.commit((m) => {
        var data = m.linkDataArray[0];  // get the first link data
      }
      );
      return result;
    });```
in the above one i'm getting error linkDataArray not exist.

Have you read https://gojs.net/latest/intro/validation.html#TextEditingValidation ?

The predicate function must return true or false, depending on whether the string resulting from the editing is permitted by your app. It must not have any side-effects. https://gojs.net/latest/api/symbols/TextBlock.html#textValidation

m.linkDataArray[0]

validations working fine, here accessing linkdataArray, giving error, linkDataArray property doesn’t exist

I repeat: you must not modify any state in a validation predicate, so do not call Model.commit. And I don’t see how result makes any sense, unless you elided some code.

Is the value of m not an instance of GraphLinksModel?

i’m updating in updatetextfunction, but error is resolved in typescript by using

if(m instanceof go.GraphLinksModel ) {
  m.linkDataArray
}

If you had stated that it was a compile-time error, not a run-time error, your question would have been a lot clearer and I could have given you the answer much quicker.

In fact, I think there was no indication that the code is TypeScript.