分配给布尔值的变量不会回显到 PHP 中的网页

Question

I have some PHP code that is supposed to check if a certain value in the $_GET global is assigned. If it isn't it automatically puts a predetermined value. If there is, it assigns the variable with a default value:

<?php
if(!isset($spaceObjects)){
  $spaceObjects = 0;
} else{
  $spaceObjects = $_GET['spaceObjects'] == true;
}
if(!isset($numOfStars)){
  $numOfStars = 100;
} else{
  $numOfStars = intal($_GET['numOfStars']);
}
if(!isset($starTwinkles)){
  $starTwinkles = 0;
} else{
  $starTwinkles = ($_GET ['starTwinkles'] == true);
}
if(!isset($numOfMeteorsMax)){
  $numOfMeteorsMax = 8;
} else{
  $numOfMeteorsMax = intval($_GET['numOfMeteorsMax']);
}
if(!isset($twinklePausing)){
  $twinklePausing = 1;
} else{
  $twinklePausing = ($_GET['twinklePausing'] == true);
}
if(!isset($nightCycle)){
  $nightCycle = 0;
} else{
  $nightCycle = ($_GET['nightCycle'] == true);
}
if(!isset($music)){
  $music = 1;
} else{
  $music = ($_GET['musicEnabled'] == true);
}
if(!isset($nightSounds)){
  $nightSounds = 0;
} else{
  $nightSounds = ($_GET['nightSounds'] == true);
}
if(!isset($nightSoundsVol)){
  $nightSoundsVol = 0.1;
} else{
  $nightSoundsVol = intval($GET['nightSoundsVol']);
}
?>
let controlVariables = {
  spaceObjects: <?php echo $spaceObjects;?>,
  numOfStars: <?php echo $numOfStars;?>,
  starTwinkles: <?php echo $starTwinkles;?>,
  numOfMeteorsMax: <?php echo $numOfMeteorsMax;?>,
  disableTwinklingWhileSpaceObjectGenerated: <?php echo $twinklePausing;?>,
  nightCycle: <?php echo $nightCycle;?>,
  music: <?php echo $music;?>,
  nightSounds: <?php echo $nightSounds;?>,
  nightSoundsVol: <?php echo $nightSoundsVol;?>
};

What's weird is that PHP is giving me nothing in some of the echo statements, causing JS to throw a syntax error.

Why instead of printing true or false PHP is giving me nothing for some fields?

Answer 1

Try to replace echo with condition to output specific text instead of variable itself. Echoed boolean outputs 1 when true, nothing when variable is false. eg:

let controlVariables = {
    spaceObjects: <?php echo ($spaceObjects)? 'true' : 'false';?>,
...
}