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Techy Treasures #1: Feelin’ Empty

    James Edwards
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    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!