Updating of variants OnInit - Angular 2

I have the variable:

compromissoInicio = ‘’;

No onInit , I have:

this.enviaForm(this.funcoes.homeAtualiza);

That is, if homeAtualiza is true , the system updates the information as follows:

... submita form ...
this.compromissoInicio = retorno[‘compromisso_inicio’];

In HTML, I have:

{{ compromissoInicio | date:‘dd/MM/yyyy HH:mm:ss’ }}

The problem is that if homeAtualiza is true , every time you return to the home page, the system will unnecessarily query the webservice.

And, if homeAtualiza is false , the content of {{ compromissoInicio | date:‘dd/MM/yyyy HH:mm:ss’ }} is empty.

I need a way that compromissoInicio always stays with the last content loaded, if the page is not updated, in onInit .