"Click" the applicable donation amount on a Salsa donation page when passing an amount via the URL. Also saves the amount so that it appears when errors happen on a donation page.

passing_an_amount_to_a_donation_page.html

    <script type="text/javascript">
        (function () {
            // SalsaStaff 81331: If "amount=number" is in the URL, then click the radio button
            // for that amount. If a radio button does not exist, then put 'number' into the
            // "other" field. 
            //
            // This script captures the amount at submit and stores it in the browser's local
            // storage. If there are errors passed back from Salsa, then the amount is retrieved
            // from the browser's local storage. Local storage is cleaned after retrieving the value.
            // 
            // If there's not an  'amount' parameter in the URL, *and* there not an amount in local
            // storage, then then a default radio button is checked (nominally $50).
            //

            // Function to search the donation page for an amount.
            // @return  Number|null  Value for the amount
            function getAmount() {
                var amount = parseFloat(document.querySelector("#otheramt").value);
                if (isNaN(amount)) {
                        amount = Array.from(document.querySelectorAll('input[name="amount"]'))
                        .filter(function(e) { return e.checked; })
                        .reduce(function(a, e) { a = e.value; return a; }, 0);
                };
                return amount;
            }

            // Function to click the radio button for amount the provided amount.  If
            // no radio button exists, then put the amount into the "other amount" field.
            // @param  Number  a  amount to store
            function setAmount(amount) {
                if (!isNaN(amount)) {
                    var otherAmount = document.querySelector("#otheramt");
                    var field = document.querySelector("#amt" + amount);
                    if (field != null) {
                        field.click();
                        otherAmount.value = '';
                    } else {
                        document.querySelector('#other').click();
                        otherAmount.click();
                        otherAmount.value = amount;
                    }
                }
            }

            $(document).ready(function () {
                var defaultAmount = 50;
                if (document.querySelector('input[name="donate_page_KEY"]') != null) {
                    var m = RegExp('amount=(\\d+)').exec(window.location.search);
                    var amount = (m != null) ? m[1] : defaultAmount;
                    // If there are errors, then it's time to retrieve the amount
                    // from localStorage.
                    if ($('.error').length > 0) {
                        var x = window.localStorage.getItem('abc');
                        console.log('Retrieved ' + x);
                        if (x != null) {
                            window.localStorage.removeItem('abc');
                            var a = parseFloat(x);
                            amount = !isNaN(a) ? a : amount;
                        }
                    }
                    setAmount(amount);

                    $('.salsa form').submit(function(e) {
                        // e.preventDefault();
                        amount = getAmount();
                        if (!isNaN(amount)) {
                            window.localStorage.setItem('abc', '' + amount);
                            console.log('Stashing ' + amount);
                        }
                        return true;
                    })
                }
            });
        })();
    </script>

One problem that's just come up with this is that when a supporter gets an error (because they mis-typed credit card or something), their donation amount resets to this default, rather than what they already selected before their initial attempt to submit. Is there a quick fix?

Hi, Sarah! Fixed that in the most recent release. You'll need to replace the whole script in order to take advantage of the change.