Cannot set property 'elements' of undefined - Array in Angular

Question

I got the following error with my code.

"Cannot set property 'elements' of undefined"

Code looks like this:

this.languages.forEach((value, index) => {
  debugger
  this.languageTableElement = { type: 'checkbox'}
  this.languageTableRows[index].elements.push(this.languageTableElement)
})

The question is: How to define the elements ?

Answer 1

Ok, i reconized how to do it, the answer is simple:

this.languageTableRows = [];
    
    this.languages = await this.languageService.getAllLanguages().toPromise();

    this.languages.forEach((value, index) => {
      this.languageTableRows[index] = new TableRowModel;
      this.languageTableRows[index].elements = [];
      this.languageTableElement = { type: 'checkbox'}

      this.languageTableRows[index].elements.push(this.languageTableElement)
    })