Letter limit and move to other box Adobe Animate HTML5 Canvas

that's a mistake.  (using a textinput component.)  as mentioned before you should be using a dynamic textfield.

but if that's what you want, this will do what you want and set you up to continue to the next problem:

this.focusA = [];

document.addEventListener('keyup', f.bind(this));

function drawEndF(){
this.focusA.push(document.getElementById("ti_1"));  // where ti_1 is a text input component.  you'll want to loop through them all here
}

stage.on("drawend", drawEndF, this, true);

function f(e){
for(var i=0;i<focusA.length;i++){
if(this.focusA[i] == document.activeElement){
this.focusA[i].value = this.focusA[i].value.slice(-1);
}
}
}