Setting the value of a javascript variable if null

Question

I am setting 3 global variables to the values of my posts meta data. I would like to understand how to set a default value for each variable if none is returned.

<script type="text/javascript">
var JprettyAd = '<?php echo get_post_meta($post->ID, 'prettyAd', true); ?>';
var JprettyName = '<?php get_post_meta($post->ID, 'prettyName', true); ?>';
var JprettyLink = '<?php get_post_meta($post->ID, 'prettyLink', true); ?>';
</script>

You can't, if php returns null, the value will be 'null', a string is never false or null, unless the php returns an empty string. If the ouput looks like this: var JprettyAd = '';, you could can simply add the default operator: var JprettyAd = '<?php echo get_post_meta($post->ID, 'prettyAd', true); ?>' || 'defaultString'; — Elias Van Ootegem
– Elias Van Ootegem, Commented Aug 27, 2012 at 15:23
better run that php output through json_encode(), unless you enjoy having your JS code injected and killed due to syntax errors. — Marc B
– Marc B, Commented Aug 27, 2012 at 15:49

jbabey · Accepted Answer · 2012-08-27 15:30:10Z

4

var JprettyAd = <?php echo get_post_meta($post->ID, 'prettyAd', true); ?> ||
    'someDefault';

Note this will use the 'someDefault' value if PHP returns any "falsey" value: null, undefined, '', 0, or NaN.

See the section labeled "Default Assignments" here.

answered Aug 27, 2012 at 15:30

jbabey

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2 Comments

slebetman Over a year ago

You should quote the <php..> otherwise it may be interpreted as a variable name and error out. Unless you're sure that the value is a number.

Jon Smith Over a year ago

Thank you. With a small tweak this works perfectly. All that was need was to add single quotes around php and change the key quotes to double.

TigOldBitties · Accepted Answer · 2012-08-27 15:36:26Z

0

get_post_meta returns an empty array if not found so you can do

<?php $response = get_post_meta($post->ID, 'prettyAd', true); ?>
var JprettyAd = <?php echo ($response ?: $defaultValue); ?>;

because empty arrays in php are evaluated as false

answered Aug 27, 2012 at 15:36

TigOldBitties

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