export default function load(src, opts, cb) {
	var head = document.head || document.getElementsByTagName('head')[0];
	var script = document.createElement('script');
	if (typeof opts === 'function') {
		cb = opts;
		opts = {};
	}
	opts = opts || {};
	cb = cb || function () {};
	script.type = opts.type || 'text/javascript';
	script.charset = opts.charset || 'utf8';
	script.async = 'async' in opts ? !!opts.async : true;
	script.src = src;
	if (opts.attrs) {
		setAttributes(script, opts.attrs);
	}
	if (opts.text) {
		script.text = '' + opts.text;
	}
	var onend = 'onload' in script ? stdOnEnd : ieOnEnd;
	onend(script, cb);
	// some good legacy browsers (firefox) fail the 'in' detection above
	// so as a fallback we always set onload
	// old IE will ignore this and new IE will set onload
	if (!script.onload) {
		stdOnEnd(script, cb);
	}
	head.appendChild(script);
}
function setAttributes(script, attrs) {
	for (var attr in attrs) {
		script.setAttribute(attr, attrs[attr]);
	}
}
function stdOnEnd(script, cb) {
	script.onload = function () {
		this.onerror = this.onload = null;
		cb(null, script);
	};
	script.onerror = function () {
		// this.onload = null here is necessary
		// because even IE9 works not like others
		this.onerror = this.onload = null;
		cb(new Error('Failed to load ' + this.src), script);
	};
}
function ieOnEnd(script, cb) {
	script.onreadystatechange = function () {
		if (this.readyState != 'complete' && this.readyState != 'loaded') return;
		this.onreadystatechange = null;
		cb(null, script); // there is no way to catch loading errors in IE8
	};
}