简单的按钮即可检查JavaScript中的表单验证

Question

I'm just trying to create a simple button to check if an input field is empty and style it accordingly. I feel like this should be really simple but I'm just missing something.

<input id="text"></input>
<button id="button">check</button>
<script>
var text = document.getElementById('text');
var button = document.getElementById('button');

function checker() {
   if (text.value === "") {
    text.style.cssText = "background:red;";
    return false;
   }
   else {
       text.style.cssText = "background:green;";
   }
}

button.addEventListener("click", checker(), false);
</script>

And here's the link to a jsfiddle that I was using to try and get it to work.

Link

Answer 1

Instead of passing a reference to the checker() function, you are actually calling the function and passing the result.

What you want to do is pass a reference to the function like this...

button.addEventListener("click", checker, false);

Note the lack of ()

Answer 2

You need to pass the function by reference:

button.addEventListener("click", checker, false);

Note: you could also pass an anonymous function:

button.addEventListener("click", function(){checker();}, false);