---
layout: page
title: "JavaScript defined function"
comments: true
sharing: true
footer: true
alias:
- /functions/view/defined:385
- /functions/view/defined
- /functions/view/385
- /functions/defined:385
- /functions/385
---
<!-- Generated by Rakefile:build -->
A JavaScript equivalent of PHP's defined

{% codeblock misc/defined.js lang:js https://raw.github.com/kvz/phpjs/master/functions/misc/defined.js raw on github %}
function defined (constant_name) {
  // http://kevin.vanzonneveld.net
  // +   original by: Waldo Malqui Silva
  // +   improved by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)
  // +    revised by: Brett Zamir (http://brett-zamir.me)
  // %          note 1: Because this function can (albeit only temporarily) overwrite a global variable,
  // %          note 1: it is not thread-safe (normally not a concern for JavaScript, but would be if used
  // %          note 1: in a threaded environment, e.g., DOM worker threads)
  // *     example 1: defined('IMAGINARY_CONSTANT1');
  // *     returns 1: false
  var tmp = this.window[constant_name];

  this.window[constant_name] = this.window[constant_name] ? 'changed' + this.window[constant_name].toString() : 'changed';
  var returnval = this.window[constant_name] === tmp;
  if (!returnval) { // Reset
    this.window[constant_name] = tmp;
  }

  return returnval;
}
{% endcodeblock %}

 - [view on github](https://github.com/kvz/phpjs/blob/master/functions/misc/defined.js)
 - [edit on github](https://github.com/kvz/phpjs/edit/master/functions/misc/defined.js)

### Example 1
This code
{% codeblock lang:js example %}
defined('IMAGINARY_CONSTANT1');
{% endcodeblock %}

Should return
{% codeblock lang:js returns %}
false
{% endcodeblock %}


### Other PHP functions in the misc extension
{% render_partial _includes/custom/misc.html %}