To find the text visible on a button in JavaScript, use the innerHTML property.
Example
You can try to run the following code to learn how to display the text visible −
<!DOCTYPE html>
<html>
<body>
<form id = "myForm">
<button id = "btn" type = "button">My Button</button>
</form>
<script>
var str = document.getElementById("btn").innerHTML;
document.write("Button text: "+str);
</script>
</body>
</html>