使用javascript中的document.querySelector在数组中获取值时错误NULL？

Question

object = ["a","input","textarea","select","img","#content",".view"];
for (var i = 0; i < oj.length; i++) {
    var resources = document.querySelector(object[i]);
    resources.addEventListener('mouseover', function(){alert("test");}, false);
}

Error TypeError: resources is null , how to fix it ?

Answer 1

I guess the basic check for non-falsy value (element matched the selector) is the way to go:

if (resources) {
    resources.addEventListener("mouseover", function() { ... }, false);
}

Answer 2

There are no elements matching one of the selectors in your array. Do a simple check to make sure its not undefined, before attaching the event.

var object = ["a","input","textarea","select","img","#content",".view"];
for (var i = 0; i < oj.length; i++) {
    var resources = document.querySelector(object[i]);
    if(resources){
    resources.addEventListener('mouseover', function(){alert("test");}, false);
    }
}