How to make text show in canvas when submit is clicked in JS?

Question

JavaScript

I have a form, using jQuery I take data from the field
var stHeader = $('#stHeader').val();
And there is a function that displays this text in the canvas when clicked on submit in which onclick="stGenerate()"
Here is the function

function stGenerate() {
      Header.font = '12px Arial';
      Header.fillStyle = '#cfcdcb';
      Header.fillText(stHeader, 88, 27);
  }

But when you click on the button, the text appears and immediately disappears, how to fix it? Thanks in advance