Angular states?

hi i have this code

  this.serve.mewt.forEach(function(data) {
    let x = data['1. open'];
  return this.arabic},this)
My problem is that when angular runs arabic is undefined or an empty array.
If I set an intervall I end up with mew function feeding array every two seconds instead with duplicate data.
How can I do so that function is executed once only and wait for data to be ready?