Unable to store value into global variable from anonymous function - Javascript and Protractor

Question

I am writing Protractor scripts. My issue is, I am unable to store value into global variables. Neither into global.somevariable, nor into browser.params.somevariable.

I have 2 files: 1. login.js 2. helper.js

From a anonymous method which is inside of helper.js file, I am trying to store the value into a global variable. I am calling this helper.js related method from a js file which is a PageObject file.

In config.js, I declared 2 variables - One with global keyword. Second one with, onPrepare() method,so I can use browser.params.someVar. However, nothing is working.

Inside of that method, the values inside of the vairables are fine. However, when I access the same variables outside of that helper.js, they are null/not correct.

config.js

exports.config =
{
  params: 
    {
      tempVar:false
    },

  onPrepare:function()
    {
      global.result=false;  
    }
};

loginpage.js

var loginPage = function() 
{
    var un = element(by.id('un'));
    var helper = new help();

    helper.verifyElemExists(un);  
    console.log(global.result);//False,though promise returned true 
    console.log(browser.params.tempVar); // This is also false
    if(global.result===true)
     {
      // Code will do something...
     }
}
module.exports =   login;

helper.js

var helper  = function()
{
  verifyElemExists = function(elem)
  {        
   elem.isPresent().then(function(res)
   {  
     browser.params.tempVar=res;
     global.result =res;             
   }); 
}
module.exports =   helper;

Looks like your .isPresent() method returns a Promise, which means it's asynchronous. It returns immediately, and when its work completes later the function passed into .then() will be called. — Pointy
– Pointy, Commented Jan 6, 2019 at 14:53
Yes Pointy, not sure how to make this work, first the variables are called, then the anonymous function is called - this is making my tests fail. — user3055964
– user3055964, Commented Jan 6, 2019 at 15:10

yong · Accepted Answer · 2019-01-07 03:11:33Z

You need to know the process of nodejs executing protractor script. The root cause of your issue comes from following code snippet:

helper.verifyElemExists(un);  
// when nodejs execute above line, all promises generated in this function 
// will be added into a list (you can call the list as protractor control flow),
// after all sync script be executed, the protractor control flow start to execute 
// the promise in the list one by one in the order as they are added into list.

console.log(global.result); 
console.log(browser.params.tempVar);
if(global.result===true)
{
  // Code will do something...
}
// when nodejs execute above lines, because all of them are sync script,
// the execution result of then return immediately, and at the time point they are executed, 
// the promise of `helper.verifyElemExists(un);`
// have not start to execute(or not complete execute), 
// thus the `global.result` and `browser.params.tempVar` are still with init value: false

From above protractor script execution process, you can see when promise and sync code executing complete, a promise list will be created for promise code, but not for sync code. Then promises in list are executed.

To fix your issue, you can wrap above sync code into a promise, so that they are executed after the promise generated in helper.verifyElemExists(un);

helper.verifyElemExists(un); 

// browser.getTitle() is a promise which be added into promise list after
// helper.verifyElemExists(un);
browser.getTitle().then(function(){
    console.log(global.result); 
    console.log(browser.params.tempVar);
    if(global.result===true)
    {
      // Code will do something...
    }
})


// or change the `helper.verifyElemExists()` to return a promise
var helper  = function()
{
  verifyElemExists = function(elem)
  {        
   return elem.isPresent().then(function(res)
   {  
     browser.params.tempVar=res;
     global.result =res;             
   }); 
}
module.exports = helper;


helper.verifyElemExists(un).then(function(){
    console.log(global.result); 
    console.log(browser.params.tempVar);
    if(global.result===true)
    {
      // Code will do something...
    }   
})

Thanks Yong, for your exceptionally well written answer - It resolved my issue. I struggled 4 hours to resolve this.

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