How to add javascript into php?

Here is my js code

<script>
function myform() {
    var n = document.getElementById("name").value;

    if (n == "") {
        document.getElementById("username").innerHTML = "Please enter your name";
        return false;
    }
    if (!isNaN(n)) {
        document.getElementById("username").innerHTML = "Please enter valid name";
        return false;
    }
}
</script>

How to write this js code into php

m trying all code in echo but not working plz help

after php echo using

    echo'<script>
function myform() {
    var n = document.getElementById("name").value;

    if (n == "") {
        document.getElementById("username").innerHTML = "Please enter your name";
        return false;
    }
    if (!isNaN(n)) {
        document.getElementById("username").innerHTML = "Please enter valid name";
        return false;
    }
}
</script>';

thankyou

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