angularjs: controller hijacking another controller's variable - angularjs

Question

I am facing a very strange issue with variable in one controller being hijacked by another controller. Here are the details:
In my HTML I have two ng-view tags. Each tag leads to a templateURL (an html) that has its own corresponding controller. Ctrl1 and Ctrl2
the two ng-views are at the same level in the html hierarchy - that is, one is NOT the child of another
Controller1 looks like this:
ngEpMod.controller('Ctrl1',[function() {
selfX = this;
abc = 'abc controller1';
console.log(abc); // break point 1
selfX.query = function() {
console.log("abc=");
console.log(abc); // break point 2
console.log("search query=");
console.log(selfX.searchQ);
lySP.searchHomes();
};
}]);
Controller2 looks like this:
ngEpMod.controller('Ctrl2',[function() {
self = this;
abc = 'abc controller2';
}]);
Both controllers are associated in the html using a "controller as" syntax.
The query() method in Ctrl1 is fired when user user clicks a button (ng-click)
Mystery: As I load the html page ($state) that has the two ng-views, I am observing the browser console. I note that abc value at break-point1 is "abc controller1", but when the query() method is fired, it mysteriously changes to "abc controller2". There is no global variable by that name! As I understand, when the page is being laid out, Ctrl1 is created first so at break-point 1 abc has the correct value, then Ctrl2 is created and somehow it high-jacks the abc variable! Stranger even is that I noticed this problem first with my self variable (self = this) and then I introduced abc just for additional check
Gurus, I am a newbie and would really appreciate your help.

Answer 1

By creating a variable without var (or let in ES6), you've created a global variable attached to window:
abc = 'abc controller1'; equals to window.abc = 'abc controller1';
When the 1st controller instantiates it declares the variable abc on window. When the 2nd controller instantiates, it changes the global abc variable content.
To avoid it in this case define var abc in both controllers.
To avoid it in the future add 'use strict'; to each function deceleration, for example:
ngEpMod.controller('Ctrl2',[function() {
'use strict';
self = this;
var abc = 'abc controller2';
}]);
Strict mode will throw error when you make this mistake (any many others). From MDN:
First, strict mode makes it impossible to accidentally create global
variables. In normal JavaScript mistyping a variable in an assignment
creates a new property on the global object and continues to "work"
(although future failure is possible: likely, in modern JavaScript).
Assignments which would accidentally create global variables instead
throw in strict mode:

Answer 2

I would drop the below code into your app above this instantiation (most modern browsers should understand this syntax for debugging). Call window.trackCtrl in every controller constructor and then pop open the console in chrome or firefox and type printCtrls() and you should get a print out of when they were created in order.
window.trackCtrl = (name) => {
var newCtrl = {}
newCtrl.name = name + '_' + performance.now()
window.trackingCtrls = window.trackingCtrls || []
window.trackingCtrls.push(newCtrl)
}
window.printCtrls = () => Array.isArray(window.trackCtrls) ? window.trackingCtrls.forEach(x => console.info(x)) : console.error('trackCtrls not defined')
This will find bugs such as the controllers getting loaded out of order or duplicate copies of your code or libraries getting loaded on the same page. Performance API helps a lot in these situations => https://developer.mozilla.org/en-US/docs/Web/API/Performance/now