These are some quick "coppy-and-paste" snippets that I use all the time.

PHP. Report All PHP Errors

error_reporting(E_ALL);
ini_set('display_errors', true);
ini_set('display_startup_errors', true);

Composer. As Lean and Minimal As Possible

composer update --prefer-dist -o -vvv --profile

PHP. XML to Array

function xmlToArray($xml) {
    if (is_string($xml)) {
        $sml = simplexml_load_string($xml, 'SimpleXMLElement', LIBXML_NOCDATA);
    }

    $array = [];
    $array['TagName'] = $xml->getName();
    $array['TagText'] = trim((string) $xml);
    $array['TagAttributes'] = array();
    $array['TagChildren'] = array();

    foreach ($xml->attributes() as $k => $v) {
        $array['TagAttributes'][$k] = (string) $v;
    }

    foreach ($xml->children() as $k => $v) {
        $array['TagChildren'][] = xmlToArray($v);
    }

    return $array;
}

Get Content Between Two X/HTML Tags

function getTagsContent($string, $tagname) {
    $pattern = "/<$tagname ?.*>(.*)<\/$tagname>/";
    preg_match($pattern, $string, $matches); 
    return $matches[1];
}

PHP. Is it a POST request?

$isPost = $_SERVER['REQUEST_METHOD'] == "POST" ? true : false;

Linux. Creating Swap File

free -m
/bin/dd if=/dev/zero of=/var/swap.1 bs=1M count=1024 // 1GB, or
/bin/dd if=/dev/zero of=/var/swap.1 bs=1M count=2048 // 2GB
/sbin/mkswap /var/swap.1
/sbin/swapon /var/swap.1

# Now add an entry to your /etc/fstab file to persist the change

/var/swap.1 none swap sw 0 0

JavaScript. Find Number of Days in Date Range

function numberOfDaysInDaterange(date1, date2) {
        var _MS_PER_DAY = 1000 * 60 * 60 * 24;
        var utc1 = Date.UTC(date1.getFullYear(), date1.getMonth(), date1.getDate());
        var utc2 = Date.UTC(date2.getFullYear(), date2.getMonth(), date2.getDate());

        return Math.floor((utc2 - utc1) / _MS_PER_DAY);

}

JavaScript. Limit User Entered Text to Numeric Values Only

$(function () {
    $('form[name=FORM_.EDIT] input[name=Price]').keyup(function () {
        var numeric = $.trim($('form[name=FORM_.EDIT] input[name=Price]').val());

        numeric = numeric.replace(/[^0-9.]/g, '');
        $('form[name=FORM_.EDIT] input[name=Price]').val(numeric);
    });
});

PHP. Find Number of Days in Date Range

function numberOfDaysInDaterange($time_start, $time_end) {
        $time_start = is_numeric($time_start) ? $time_start : strtotime($time_start);
        $time_end = is_numeric($time_end) ? $time_end : strtotime($time_end);
        $time_start = mktime(0, 0, 0, date('m', $time_start), date('d', $time_start), date('Y', $time_start));
        $time_end = mktime(0, 0, 0, date('m', $time_end), date('d', $time_end), date('Y', $time_end));
        $range = array();
        if ($time_start <= $time_end) {
            $range[] = date('Y-m-d', $time_start);
            while ($time_start < $time_end) {
                $time_start += 86400; // add 24 hours
                $range[] = date('Y-m-d', $time_start);
            }
        }
        return $range;
}

JavaScript. remove checkboxes being arrays in WP

function formatInput (selector) {
    var array = $(selector + ' :input').serializeArray();
    var json = {};

    jQuery.each(array, function () {
        var name = $.trim(this.name.split('[').join('').split(']').join().split(',').join('')); // Remove checkboxes being arrays in the WP plugin
        json[name] = this.value || '';
    });


    return json;
}

JavaScript. Complete All Promises and Resolve

/**
* Complete all promises
* @param items An array of items.
* @param fn A function that accepts an item from the array and returns a promise.
* @returns {Promise}
*/
function forEachPromise(items, fn) {
    return items.reduce(function (promise, item) {
        return promise.then(function () {
            return fn(item);
        });
    }, Promise.resolve());
}

JavaScript. Simple Template Function

function getTemplate(data) {
    var data = typeof data === "undefined" ? {} : data;
    if (typeof data['QUESTION'] === "undefined") {
            data['QUESTION'] = "Enter Your Question";
    }
    if (typeof data['QUESTION_ID'] === "undefined") {
        data['QUESTION_ID'] = ('new_' + Math.floor(Math.random() * 999999999));
    }
    var tpl = $('#QuestionTemplate').html();
    $.each(data, function (key, value) {
        tpl = tpl.split('$$' + key + '$$').join(value);
    });
    tpl = tpl.replace(new RegExp("\\$\\$.*\\$\\$", "g"), "");
    return tpl;
}