QSUtils: a query-string utility for browser/client-side JavaScript. supports case-insensitive, truthy, typed values, defaults. (demo: https://qsutils.glitch.me/)

qsutils.js

/**
 * QSUtils: a query-string utility for browser/client-side JavaScript.
 *
 * supports case-insensitive, truthy, typed values, defaults.
 *
 * demo: https://qsutils.glitch.me/
 */
class QSUtils {
  constructor () {
    this.qs = new URLSearchParams(window.location.search);
  }

  get (key, {caseSensitive = false, truthy = false, type = 'string', defaultValue = null} = {}) {
    let value = this.qs.get(key);
    if (value !== null && !caseSensitive) {
      const keyLower = key.toLowerCase();
      for (let [qsKey, qsValue] of this.qs.entries()) {
        if (keyLower === qsKey.toLowerCase()) {
          value = qsValue;
          break;
        }
      }
    }
    if (defaultValue !== null && typeof type !== defaultValue) {
      type = typeof defaultValue;
    }
    if (truthy) {
      value = this.getTruthyValue(value);
    }
    if (type === 'boolean' && defaultValue !== null && value === false) {
      value = defaultValue;
    } else if (typeof value !== type) {
      if (type === 'integer') {
        value = parseInt(value, 10);
        if (defaultValue !== null && !Number.isInteger(value)) {
          value = defaultValue;
        }
      } else if (type === 'number' || type === 'float') {
        value = parseFloat(value);
        if (defaultValue !== null && !Number.isFinite(value)) {
          value = defaultValue;
        }
      } else if (type === 'boolean') {
        if (defaultValue !== null && value === false) {
          value = defaultValue;
        }
      }
    }
    return value;
  }

  getTruthy (key, opts) {
    opts = Object.assign({}, opts, {truthy: true, type: 'boolean'});
    return this.get(key, opts);
  }

  getTruthyValue (value) {
    if (typeof value !== 'string') {
      return false;
    }
    const valueLower = value.toLowerCase();
    return valueLower === '' || valueLower === '1' || valueLower === 'true' || valueLower === 'yes' || valueLower === 'y' || valueLower === 'on';
  }
}

const qs = 'fruit=apple&log=0&verboselog=';
const qsu = new QSUtils(qs);
console.log(qs);
console.log({
  debug: qsu.getTruthy('debug', {defaultValue: true}),
  fruit: qsu.get('fruit'),
  hasVegetable: qsu.getTruthy('hasVegetable', {defaultValue: 'nope'}),
  vegetable: qsu.get('vegetable', {defaultValue: 'a vegetable'}),
  log: qsu.getTruthy('log'),
  verboseLog: qsu.getTruthy('verboseLog')
});