//移除脚本的时候把函数也注销掉。
var btn = document.getElementsByTagName('button')[0];
var tip = true;
btn.onclick = function() {
    if (tip === true) {
        var sp = document.createElement('script');
        sp.textContent = "var time='';" +
            "var num=1;" +
            "function test(){console.log(num);num++;setTimeout(test,1000);}" +
            "test();";
        sp.id = 'test';
        document.head.appendChild(sp); 
        tip = false;
    } else if (tip === false) {
        tip = null;
        document.head.removeChild(document.getElementById('test'));
        test=null;//注销
    } else {
        return;
    }
}