JS function REST api call from button click

api_call_function.js

// javascript: 
function ApiCall() {
    var xhttp = new XMLHttpRequest();
    xhttp.open("POST", "REST URL HERE", true);
    xhttp.setRequestHeader("Content-type", "application/json");
    xhttp.send();
    var response = JSON.parse(xhttp.responseText);
}

// Corresponding HTML button action:
<button type="submit" onclick="ApiCall()">Search</button>