ionic-framework/core/src/global/config.ts

import { IonicConfig } from '../interface';

export class Config {

  private m: Map<keyof IonicConfig, any>;

  constructor(configObj: IonicConfig) {
    this.m = new Map<keyof IonicConfig, any>(Object.entries(configObj) as any);
  }

  get(key: keyof IonicConfig, fallback?: any): any {
    const value = this.m.get(key);
    return (value !== undefined) ? value : fallback;
  }

  getBoolean(key: keyof IonicConfig, fallback = false): boolean {
    const val = this.m.get(key);
    if (val === undefined) {
      return fallback;
    }
    if (typeof val === 'string') {
      return val === 'true';
    }
    return !!val;
  }

  getNumber(key: keyof IonicConfig, fallback?: number): number {
    const val = parseFloat(this.m.get(key));
    return isNaN(val) ? (fallback !== undefined ? fallback : NaN) : val;
  }

  set(key: keyof IonicConfig, value: any) {
    this.m.set(key, value);
  }
}

const IONIC_PREFIX = 'ionic:';
const IONIC_SESSION_KEY = 'ionic-persist-config';

export function configFromSession(): any {
  try {
    const configStr = window.sessionStorage.getItem(IONIC_SESSION_KEY);
    return configStr !== null ? JSON.parse(configStr) : {};
  } catch (e) {
    return {};
  }
}

export function saveConfig(config: any) {
  try {
    window.sessionStorage.setItem(IONIC_SESSION_KEY, JSON.stringify(config));
  } catch (e) {
    return;
  }
}

export function configFromURL() {
  const config: any = {};
  const win = window;
  win.location.search.slice(1)
    .split('&')
    .map(entry => entry.split('='))
    .map(([key, value]) => [decodeURIComponent(key), decodeURIComponent(value)])
    .filter(([key]) => startsWith(key, IONIC_PREFIX))
    .map(([key, value]) => [key.slice(IONIC_PREFIX.length), value])
    .forEach(([key, value]) => {
      config[key] = value;
    });

  return config;
}

function startsWith(input: string, search: string): boolean {
  return input.substr(0, search.length) === search;
}