JS Toggle Div on Button Onclick

js_toggle_div.js

<div id="target_div_id"></div>
<button id='button_id'>Click</button>

var button = document.getElementById('button_id');

button.onclick = function() {
    var div = document.getElementById('target_div_id');
    if (div.style.display !== 'none') {
        div.style.display = 'none';
    }
    else {
        div.style.display = 'block';
    }
};