URLSearchParams polyfill in es6, licensed MIT

URLSearchParams.js

class URLSearchParams {
    constructor(str) {
        if (str) this._parse(str);
    }

    _getStr(key) {
        return Array.isArray(this[key]) ? this[key].map(value => `${key}=${encodeURIComponent(value)}`).join('&') : `${key}=${encodeURIComponent(this[key])}`;
    }

    _parse(str) {
        if (!str) return false;
        if (str.charAt(0) === '?') str = str.substr(1);
        str.split('&').map(e => e.split('=')).forEach(e => this.append(e[0], e[1]));
        return this;
    }

    append(key, value) {
        value = decodeURIComponent(value);
        if (this.has(key))
            this[key] = [].concat(this[key]).concat(value);
        else this[key] = value;
    }

    delete(name) {
        delete this[name];
    }

    entries() {
        const arr = [];
        for (const key of this.keys()) {
            if (Array.isArray(this[key]))
                this[key].forEach(value => arr.push(key, value));
            else arr.push([key, this[key]]);
        }
        return arr;
    }

    get(name) {
        return Array.isArray(this[name]) ? this[name][0] : this[name];
    }

    getAll(name) {
        return [].concat(this[name]);
    }

    has(name) {
        return this.hasOwnProperty(name);
    }

    keys() {
        return Object.keys(this);
    }

    set(name, value) {
        this[name] = decodeURIComponent(value);
    }

    toString(keys = this.keys()) {
        keys = keys && keys.map ? keys.filter(e => this.has(e)) : this.keys();
        return keys.map(e => this._getStr(e)).join('&');
    }

    values() {
        return this.entries().map(e => e[1]);
    }
}