Hiding DOM elements with local JS scripts does not take effect

[rainstorm0506]

index.php
$localFilePath = 'F:/Phpstudy/PHPTutorial/WWW/Capture/screen/scripts/flfg.js';
$screenCapture->includeJs(new LocalPath($localFilePath));

flfg.js
(function () {
var footer = document.getElementById('zt');
console.log(footer); #result is null
})();