JavaScript - - By James Edwards

Techy Treasures #1: Feelin’ Empty

Techy Treasures is a new, regular feature where we’ll be publishing tips, tricks and code snippets for web developers. These are not blue-sky bubbles, they’re solid, proven ideas that you can use in the wild with confidence.

And to start with, a neat little function that checks whether a variable is empty, inspired by PHP’s function of the same name:

function empty(data)
{
	if(typeof data == 'undefined' || data === null) { return true; }
	else if(typeof data == 'string' && (data === '0' || data.replace(/^s+|s+$/g, '') === '')) { return true; }
	else if(typeof data == 'number' && data === 0) { return true; }
	else if(typeof data == 'boolean' && data === false) { return true; }
	else if(typeof data == 'object')
	{
		if(data instanceof Array && data.length == 0) { return true; }
		else
		{
			var n = 0;
			for(var i in data)
			{
				if(!data.hasOwnProperty(i)) { continue; }
				n++;
			}
			if(n == 0) { return true; }
		}
	}
	return false;
}

So a variable is considered empty if it’s:

  • undefined
  • null
  • a string, and its value is "0", or an empty string, or only whitespace
  • a number, and its value is 0
  • a boolean, and its value is false
  • an array, and it has no values
  • an object, and it has no enumerable properties

It works for any kind of variable, for example, used as a condition:

if(!empty(data)) 
{
	//data is not empty
}

You could even pass the return value of another process, thanks (as ever!) to JavaScript’s ability to handle almost anything as an argument:

if(!empty(function()
{
	//do some process and return a value
}))
{
	//return value was non-empty
}

I’ve been finding it particularly useful for validating function arguments, for example a simple shortcut function for getting element references:

function get(id)
{
	return document.getElementById(id);
}

But what if the id parameter is empty, or null, or not there at all? We can check all those possibilities with a single statement, and then handle the situation accordingly:

function get(id)
{
	if(empty(id)) { return null; }
	return document.getElementById(id);
}

And there you go — a neat, simple, and elegant method for validating any kind of variable.

See you soon for another Techy Treasure!

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