Переопределение функции внутри функции

Вариант 1.

var pushTheRedButton = function() {
    pushTheRedButton = function() {
        alert("Now look what you've done!");
    }
    alert("Don't ever push this button again!");
}

pushTheRedButton(); //"Don't ever push this button again!"
pushTheRedButton(); //"Now look what you've done!"

Вариант 2.

system.shutdown = function() {
    system.shutdown = function() {
        alert("don't worry - we're already processing your shutdown request");
    }
    lengthyShutdownProcess();
}

system.shutdown();
system.shutdown(); //"don't worry - we're already processing your shutdown request"

Вариант 3.

System.prototype.download = function(file) {
    this.download = function() {
         alert("still downloading");
    }
    requestDownload(file, {
        callback: function() {
            delete this.download;
        }
    });
}

Вариант 4.

var getMyText = function(myDiv) {
    getMyText =
        myDiv.innerText !== undefined ?
            function(myDiv) {return myDiv.innerText} :
            function(myDiv) {return myDiv.textContent};

    return getMyText(myDiv);
}