button copy javascript
<!DOCTYPE html>
<html>
<head>
<script>
function paste() {
var pasteText = document.querySelector("#text");
pasteText.focus();
document.execCommand("paste");
pasteText.value = pasteText.value + pasteText.value;
}
</script>
</head>
<body>
<input id="text">
<button onclick="paste()">Paste</button>
</body>
function myFunction() {
/* Get the text field */
var copyText = document.getElementById("myInput");
/* Select the text field */
copyText.select();
copyText.setSelectionRange(0, 99999); /*For mobile devices*/
/* Copy the text inside the text field */
document.execCommand("copy");
/* Alert the copied text */
alert("Copied the text: " + copyText.value);
}