小白求助一个判断位置是否在区域的代码问题！

[qmxzh]

怎样才能让这段代码的结果在html上显示?
function isInPolygon(checkPoint, polygonPoints) {
var counter = 0;
var i;
var xinters;
var p1, p2;
var pointCount = polygonPoints.length;
p1 = polygonPoints[0];
for (i = 1; i <= pointCount; i++) {
p2 = polygonPoints[i % pointCount];
if (
checkPoint[0] > Math.min(p1[0], p2[0]) &&
checkPoint[0] <= Math.max(p1[0], p2[0])
) {
if (checkPoint[1] <= Math.max(p1[1], p2[1])) {
if (p1[0] != p2[0]) {
xinters =
(checkPoint[0] - p1[0]) *
(p2[1] - p1[1]) /
(p2[0] - p1[0]) +
p1[1];
if (p1[1] == p2[1] || checkPoint[1] <= xinters) {
counter++;
}
}
}
}
p1 = p2;
}
if (counter % 2 == 0) {
return false;
} else {
return true;
}
}
isInPolygon(
[
121.65281295776367,
31.1488060025773
],
[
[
121.6444444656372,
31.152442014819357
],
[
121.65092468261719,
31.129227903837506
],
[
121.67993545532227,
31.13881543280873
],
[
121.67263984680176,
31.157546887523516
],
[
121.6444444656372,
31.152442014819357
]
]
);

[漠子凉]

	<div id="a"></div>
var a = isInPolygon()
document.querySelector('#a').innerText = a