动态合并值到对象属性-首先是未定义

Question

I have a php generated javascript code which adds attributes and values dynamically to an object. It looks something like this:

 var javascriptObject = {};

 <?php
 foreach($events as $event)
      echo 'javascriptObject[$event->date] += $event->title';
 endforeach
 ?>

Since I might have multiple events on the same date, it would add to the same object property, which is then processed by an external calendar library. Now, everything works fine. BUT, since it adds new data with += the first "undefined" value always stays in the beginning of every entry.

My question is, is there a way in Javascript to initialize an object with a default (empty or maybe null) value instead of leaving it 'undefined'? Can someone point me to a better solution?

ps: I'd really like to avoid checking for 'undefined' at every loop to keep the code clean, since it's a php generated javascript, would be a complete mess when the event list is big.

Answer 1

Just try with:

foreach ($events as $event) {
  echo 'javascriptObject[' . $event->date . '] = (javascriptObject[' . $event->date . '] || "") + "' . $event->title . '";';
}

Or even saver way:

$javascriptObject = array();
foreach ($events as $event) {
  if ( !isset($javascriptObject[ $event->date ]) ) {
    $javascriptObject[ $event->date ] = '';
  }
  $javascriptObject[ $event->date ] .= $event->title;
}

echo 'var javascriptObject = ' . json_encode($javascriptObject) . ';';