Am o eroare cand incerc sa pun un cod in javascript : Uncaught TypeError: Cannot read property 'addEventListener' of null

Codul meu:var button = document.getElementById("button");

button.addEventListener("click", function(){
console.log("button was clicked");
});

Am incercat si:var button = document.addEventListener("button");

document.getElementById('button').onclick = function() {
console.log("button was clicked");
}​;​

Dar da alta eroare: Uncaught SyntaxError: Invalid or unexpected token

Daca cineva imi poate explica si daca ma poate ajuta sa rezolv aceasta problema