Detect sub-pixel word- and letter-spacing.

subpixel-word-spacing-detect.js

var subpixelWordSpacing = false;

if (document.defaultView && document.defaultView.getComputedStyle) {
	// Store the original word spacing on the document element
	var originalWordSpacing = document.defaultView.getComputedStyle(document.documentElement, null).wordSpacing;
	
	// Set the word-spacing to half a pixel
	document.documentElement.style.wordSpacing = '0.5px';
	
	// This will return either 0px or 1px if sub-pixel word-spacing is not supported, otherwise
	// it will return 0.5px.
	subpixelWordSpacing = document.defaultView.getComputedStyle(document.documentElement, null).wordSpacing === '0.5px';
	
	// Restore the original word-spacing
	document.documentElement.style.wordSpacing = originalWordSpacing;
}

@stephen-uac, @CrocoDillon: excellent feedback! I only used this as a quick test to see if sub-pixel word spacing was supported or not. The changes you suggested make it a lot more robust. I've updated the Gist.