7. function setText(elem, text) {
if (! elem.firstChild) {
elem.appendChild(document.createTextNode(""));
}
elem.firstChild.data = text;
}
function run() {
var num =
parseInt(document.getElementById("num").value, 10);
var result = 0;
for (var i = 0; i <= num; i++) {
result += i;
}
// 計算完了
var retElem = document.getElementById("result");
setText(retElem, result.toString());
}