boilerplate.js/Boilerplate/src/js/helpers/ParameterByName.js

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// Gets Value Of A URL Parameter

/* How To Use (if current URL is https://examplesite.com/download?filetype=pdf&name=testfile)

    var filetype = getParameterByName('filetype');
    var filename = getParameterByName('name');

    console.log(filetype); // 'pdf'
    console.log(filename); // 'testfile'

    --Or provide your own url--

    var filetype = getParameterByName('filetype', 'https://examplesite.com/download?filetype=pdf&name=testfile');
    var filename = getParameterByName('name', 'https://examplesite.com/download?filetype=pdf&name=testfile');

    console.log(filetype); // 'pdf'
    console.log(filename); // 'testfile'

*/

function getParameterByName(name, url) {
    if (!name && !url) return queryParamsToObject();
    if ( isURL(name) ) return queryParamsToObject(name);
    url = url || window.location.href;
    name = name.replace(/[\[\]]/g, "\\$&");
    var regex = new RegExp("[?&]" + name + "(=([^&#]*)|&|#|$)"),
        results = regex.exec(url);
    if (!results) return null;
    if (!results[2]) return '';
    return decodeURIComponent(results[2]);

}

function checkParameterByName(key, value, url) {
    url = url || window.location.href;
    if (!value) return checkWithoutValue(key);
    try {
        var result = getParameterByName(key.toLowerCase(), url);
        if (value.toLowerCase() === result.toLowerCase()) { 
            return true;
        } else {
            return false;
        }
    } catch (error) {
        return false;
    }
    function checkWithoutValue(key) {
        if (Parameter.get()[key] === null) return false;
        if (Parameter.get()[key] === undefined) return false;
        return true;
    }
}

function removeParameterByName(key, url) {
    let replace = false;
    if (!url) {
        url = window.location.href;
        replace = true;
    }
    let a = document.createElement('a');
    a.href = url;
    let params = queryParamsToObject(a.href);
    delete params[key];
    a.href = objectToQueryString(params, a.href);
    if (replace) window.history.replaceState({}, null, a.href);
    return a.href;
}

function setParameterByName(key, value, uri) {
    if (typeof key === 'object' && !value) return objectToQueryString(key);
    if (typeof key === 'object' && value) return objectToQueryString(key, value);
    var re = new RegExp("([?&])" + key + "=.*?(&|#|$)", "i");
    let skip = true;
    if (uri) skip = false;
    uri = uri || location.href;
    if (value === undefined) {
        if (uri.match(re)) {
            skip && window.history.replaceState({}, null, uri.replace(re, '$1$2'));
            return uri.replace(re, '$1$2');
        } else {
            skip && window.history.replaceState({}, null, uri);
            return uri;
        }
    } else {
        if (uri.match(re)) {
            skip && window.history.replaceState({}, null, uri.replace(re, '$1' + key + "=" + value + '$2'));
            return uri.replace(re, '$1' + key + "=" + value + '$2');
        } else {
            var hash = '';
            if (uri.indexOf('#') !== -1) {
                hash = uri.replace(/.*#/, '#');
                uri = uri.replace(/#.*/, '');
            }
            var separator = uri.indexOf('?') !== -1 ? "&" : "?";
            skip && window.history.replaceState({}, null, uri + separator + key + "=" + value + hash);
            return uri + separator + key + "=" + value + hash;
        }
    }
}

function objectToQueryString(data, url) {

    if (url) {

        let a = document.createElement('a');
        a.href = url;
        a.search = '';
        url = a.href;
        Object.keys(data).forEach(key => url = setParameterByName(key, data[key], url));
        return encodeURI(url);

    } else {

        Object.keys(data).forEach(key => setParameterByName(key, data[key]));

    }
    
}

function queryParamsToObject(url) {   
    let a = document.createElement('a');
    a.href = url || location.href;
    let search = a.search;   
    var list = search.slice(1).split('&'),
        result = {};

    list.forEach(function(keyval) {
        keyval = keyval.split('=');
        var key = keyval[0];
        if (/\[[0-9]*\]/.test(key) === true) {
            var pkey = key.split(/\[[0-9]*\]/)[0];
            if (typeof result[pkey] === 'undefined') {
                result[pkey] = [];
            }
            result[pkey].push(decodeURIComponent(keyval[1] || ''));
        } else {
            result[key] = decodeURIComponent(keyval[1] || '');
        }
    });

    return JSON.parse(JSON.stringify(result));
}

window.Parameter = {};
window.Parameter.get = (name, url) => getParameterByName(name, url);
window.Parameter.set = (key, value, uri) => setParameterByName(key, value, uri);
window.Parameter.check = (key, value = null, url = null) => checkParameterByName(key, value, url);
window.Parameter.remove = (key, url) => removeParameterByName(key, url);