如何在页面加载时停止javascript中的警报触发，并在单击按钮时使其运行？

Question

Without using jQuery, how can I get a JavaScript alert to fire at the right time? It's currently firing when the page loads. I created a temp converter and would like the "convert to fahr" button and the "convert to cels" button to fire off the converted temps in a pop up "alert". Currently both buttons are successfully executing their respective temp conversion math functions but I'd also like to add the alerts when the buttons are clicked.

document.getElementById('convert').onclick = makeTempF();
document.getElementById('convertC').onclick = makeTempC();

function makeTempF() {
    var d, b, c;
    var f = document.getElementById('f').value;
    b = f - 32;
    c = b * 5;
    d = parseInt(c / 9);
    alert('Celsius Temperature is ' +d);
    // console.log(d);
}


function makeTempC() {
    var g, b, d;
    var c = document.getElementById('c').value;
    b = c * 9;
    d = b / 5;
    g = parseInt(d +32);
    alert('Fahrenheit Temperature is ' +g);
    // console.log(g);
}

Answer 1

Assign the callbacks, not what their invocation returns.

document.getElementById('convert').onclick = makeTempF;
document.getElementById('convertC').onclick = makeTempC;