Adding alt tags to images

This text helps screen-reading tools describe images to visually impaired readers and allows search engines to better crawl and rank your website. To add dynamically alt tags on images based on images filename I added a code below :

function removeExtension(filename){
	var lastDotPosition = filename.lastIndexOf(".");
	if (lastDotPosition === -1) return filename;
	else return filename.substr(0, lastDotPosition);
}

var imgs = document.getElementsByTagName("img");

for (var i = 0; i < imgs.length; i++) {
	var imgurl = imgs[i].src;
	var filename = imgurl.substring(imgurl.lastIndexOf('/')+1);
	var trimedFilename = filename.replace(/(\.[^/.]+)+$/, "");
	var titleAlt = trimedFilename.replace(/[_-]/g, " ");
	imgs[i].setAttribute("alt", titleAlt);
	imgs[i].setAttribute("title", titleAlt);
}