Implicit Binding

This is part of the series this keyword in Javascript

https://medium.com/@msinha2801/this-most-confused-mechanism-in-javascript-b60b3fa3de36

What if call site has a context object also called containing object?

'use strict';
function implicitInvocation(){
console.log(this.a);
}
var obj= {
    a:2,
    implicitInvocation:implicitInvocation
}
obj.implicitInvocation();

call site used obj context to reference the function implicitInvocation() so it can be mentioned that obj “contains” the function reference at the time function is called.
If there is a context object for a function reference, the implicit binding rule states that
“it’s that object should be used for the function fall’s this binding”

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Only the top/last level of an object property reference chain matters to the call site.

function implicitInvocation() {
console.log(this.a);
}
var obj2 = {
a: 10,
implicitInvocation: implicitInvocation
};
var obj1 = {
a: 2,
obj2: obj2
};
obj1.obj2.implicitInvocation();//42

What if implicit binding is lost?

function implicitInvocation() {
console.log(this.a);
}
var obj = {
a: 2,
implicitInvocation: implicitInvocation
};
var implicitBindingLost = obj.implicitInvocation;// function reference /alias !
var a = "global variable";
implicitBindingLost();//undefined
//incase of strict mode TypeError: Cannot read property 'a' of undefined

Even if implicitBindingLost appears to be a reference to obj.implicitInvocation its a reference to implicitInvocation itself.
The call site is implicitBindingLost which is plain, undecorated call and thus default binding applies here.