How to substitute an image when pressing a certain key?

Question

JavaScript

I am writing a tablet generator and I need that in the text field the entered text is displayed in a certain area of ​​\u200b\u200bthe picture, there are 3 fonts, svg letter format, you need to write that when you enter the letter "a" with pressing the "text 1" button, the picture "a1.svg" is displayed "and so the whole phrase and this text fit into the space allotted for size (decreased or increased)