Try to use document.createEvent described here https://developer.mozilla.org/en-US/docs/Web/API/document.createEvent
The code for function that simulates click should look something like this:
function simulateClick() {
var evt = document.createEvent("MouseEvents");
evt.initMouseEvent("click", true, true, window,
0, 0, 0, 0, 0, false, false, false, false, 0, null);
var a = document.getElementById("gift-close");
a.dispatchEvent(evt);
}