"undefined" variable problem

[MacDada]

I have changed somevar === undefined to 'undefined' === typeof somevar.

In older browsers undefined is not a reserved keyword and could be changed by some badly written code.

Example:

// somewhere in the user's js…
undefined = "trolololo";

// your library
function test(value) {
    if (undefined !== value) {
        console.log(value); // this will log "trolololo"
    }

    if ('undefined' === typeof value) {
        console.log(value); // this won't log "trolololo"
    }
}

test();