函数没有正确定义变量

Question

我有以下代码：

var first="";
var run=function(){

    first = document.getElementById("textbox1").value;

    if(first.substring(0,6)==="http://"){
       first=first.substring(7,first.length-1);
    }

    if (first.substring(0, 1) !== " " &&
        first !== "unrequired" && 
        first.substring(0, 7) !== "http://" &&
        first.substring(0, 8) !== "https://" && 
        first !== undefined && 
        first !== "" && 
        first.substring(0, 9) !== "chrome://" && 
        first.substring(0, 12) !== "view-source:" && 
        first.substring(0, 8) !== "file:///") {
      first="http://"+first;
    }

    if(first===""||first==="unrequired"){
       first=undefined;
    }
    if (first.substring(0,1)===" "){
       first="https://www.google.com/search?q=" + first.substring(1,first.length);
    }
    chrome.tabs.create({url:first})
};
setInterval(run,1);

但是chrome.tabs.create只有在我将其移到函数外部并且不运行该函数时才会运行。显然，函数对变量做了一些事情，但是什么呢？我甚至用警告告诉我出了什么问题