launch a mobile app from mobile web or inside wechat, or goes to app website to download

appup.js

;// to launch mobile app
var insideWeChat = typeof window.WeixinJSBridge == "object";
var isMobileDevice = 'ontouchstart' in window || /Android|webOS|iPhone|iPad|iPod|BlackBerry|BB10|IEMobile|Opera Mini/i.test(navigator.userAgent);
;(function(document, window){ //
var ua = navigator.userAgent;
var tid, callfn, duration = 1300;
function bind(el, en, fn, useCapture){
    el.addEventListener ? el.addEventListener(en, fn, useCapture||false): (el.attachEvent ? el.attachEvent('on'+en, fn) : el['on'+en]=fn);
}
function unbind(el, en, fn, useCapture){
    el.removeEventListener ? el.removeEventListener(en, fn, useCapture||false): (el.detachEvent ? el.detachEvent('on'+en, fn) : el['on'+en]=null);
}
var inWechat = insideWeChat;
bind(document, 'WeixinJSBridgeReady', function(){
    inWechat = insideWeChat = true;
});
var byId = 'getElementById';
var crEl = 'createElement';

var appScheme = 'MyApp://';
var appPackageID = '999999999'; // ios
var appPackageName = 'app.mindon.lab'; // android
var appSite = 'http://mindon.github.com';

var GooglePlayURL = "https://play.google.com/store/apps/details?id=";
if(/^zh-CN$/i.test(navigator.language)) {
    GooglePlayURL = 'http://sj.qq.com/myapp/detail.htm?apkName=';
}
var iOSAppStoreURL = "https://itunes.apple.com/app/id";

var current = {scheme: appScheme, id: appPackageID, name: appPackageName, site: appSite };

var mylauncher = document[byId]('app::launcher');
if(!mylauncher) {
    mylauncher = document[crEl]('div');
    mylauncher.style.display = 'none';
    mylauncher.id = 'app::launcher';
    if(document.body) {
        document.body.insertBefore(mylauncher, document.body.firstChild);
    }
}

function invisible(e) {
  tid && clearTimeout(tid);
  clean(e, false);
}

function clean(e, expired) {
  if( expired ) {
    // no app or expired
    callfn && callfn(false);
  } else {
    // success
    callfn && callfn(true);
  }
  unbind(window, 'pagehide', invisible, true);
  unbind(window, 'pageshow', invisible, true);
  if(tid) clearTimeout(tid);
  mylauncher.innerHTML = '';
}

function visit(u) {
  window.location.href = u;
}

function launch(scheme, cb) {
  if( mylauncher && mylauncher.childNodes.length > 0 )
    return false;

  if(!isMobileDevice) {
    return cb(false);
  }

  bind(window, 'pagehide', invisible, true);
  bind(window, 'pageshow', invisible, true);
  callfn = cb;
  var ios = /iPhone|iPad|iPod/i.test(ua);
  if( inWechat ) {
    visit(scheme);
  } else if(ios || window.chrome) {
    ios && setTimeout(function() {
        if (!document.webkitHidden)
            clean(null, true);
        else
            clean(null, false);
    }, 50);
    visit(scheme);

  //} else if(window.chrome && /android/i.test(ua)) { // failed
  //  visit('intent://scan/#Intent;scheme='+scheme.replace(/:\/\/.*/,'')+';package='+current.name+';end');

  } else {
    var fr = document[crEl]('iframe');
    fr.onload = function(){
      fr.onload = null;
      fr.parentNode.removeChild(fr);
      fr = null;
      clean(null, false);
    };
    fr.src = scheme;
    mylauncher.appendChild(fr);
  }
  var curr = +new Date();
  if(tid) clearTimeout(tid);

  tid = setTimeout(function(){
    tid = setTimeout(function(){
      if(+new Date() - curr > duration){
        clean(null, false);
      } else {
        clean(null, true);
      }
    }, duration -100);
  }, 80);
}

function gonext(ok, from) {
    if(!ok) {
      if( /Android|BlackBerry|BB10/i.test(ua) ) {
        visit(GooglePlayURL + current.name);
      } else {
        visit(iOSAppStoreURL + current.id);
      }
    } else if(from == 'wechat') {
      launch(current.scheme, gonext);
    }
}

function appup(scheme, iOsAppId, packageName, site) {
  if(scheme) current.scheme = scheme;
  if(iOsAppId) current.id = iOsAppId;
  if(packageName) current.name = packageName;
  if(site) current.site = site;
  if(!inWechat) inWechat = insideWeChat = typeof window.WeixinJSBridge == "object";
  if(inWechat) {
     WeixinJSBridge.invoke("getInstallState", {
         "packageUrl": scheme,
         "packageName": packageName
     }, function(res) {
         var err = (res.err_msg || ':').split(':')[1],
         norxp = /^(no|not_allow|access_denied)$/i;
         if (err && !norxp.test(err)) {
           gonext(true, 'wechat');
         } else {
           if(err == 'not_allow' || err == 'access_denied') {
             visit(current.site);
           } else {
             gonext(false, 'wechat');
           }
         }
     });
  } else {
    launch(scheme, gonext);
  }
}
if(!window.appup) // export active a mobile app
    window.appup = appup;
//---
})(document, window);