Question

Consider the following examples:

var company = 'Apple',
    log = console.log;

function f1() {
    log(company);
    var company = 'Twilio';
    log(company)
}

function f2() {
    log(company());

    function company() {
        return 'Zynga';
    }
}

function f3() {
    log(company());
    var company = function() { return 'RIM'; };
}

log(company);
log('---');
f1();
log('---');   
f2();
log('---');
f3();

The output from firebug is:

"Apple"
---
undefined
"Twilio"
---
"Zynga"
---
TypeError: company is not a function

So why is hoisting in f3 giving me the error while others are working just fine?

Answer 1

Let’s rewrite your f3 function to show what it would look like after variable hoisting:

function f3() {
    log(company());
    var company = function() { return 'RIM'; };
}

becomes:

function f3() {
    var company; // declaration hoisted

    log(company());
    company = function() { return 'RIM'; };
}

Now you can see that you are attempting to execute an undefined variable, not a function (hence the “not a function” error).

Note that this is difference from the output of f2 because function declarations are hoisted as a unit.