How can I disable the try it button until text is entered in input

Question

<label for="fname">Name</label>
<input type="text" id="v" name="firstname" placeholder="Your name.." required>

<button class="btn1" onclick="f()" disabled>Try it</button>

function f() {
var i;
var a = ["Se", "Q", 1];
var p = document.getElementById("v").value;
for(var i = 0; i < a.length; i++) {
if (a[i] == p) {
alert("good");
document.getElementById("no").innerHTML = "Congrats";
}
}
}

How do I remove the disabled button when 3 of those words from var a Are inputted

Answer 1

Thanks but onkeyup="f()" means what , what is the function