Edit in JSFiddle

var btn = document.getElementById("btn");
var result = document.getElementById("result");
btn.onclick = function(){
	var name = 'World!';
 (function () {
    if (typeof name === 'undefined') {
        var name = 'Jack';
        result.innerHTML = 'Goodbye ' + name;
    } else {
        result.innerHTML ='Hello ' + name;
    }
})();
}

<p>点击查看结果：</p>
<button id="btn">查看结果</button>
<p>结果：</p>
<div id="result"></div>

p {
    font-size: 14px;
    height 24px;
    line-height: 24px;
}