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// returns true if your browser supports calc()
myapp.checkCalc = function (prefix = '') {
	var el = document.createElement('div');
	el.style.cssText = prefix + 'width: calc(1px);';
	return !!el.style.length;
};

// returns true if your browser supports any version of calc(), prefixed or not
myapp.checkAllCalc = function (prefix = '') {
	return myapp.checkCalc('-webkit-') || myapp.checkCalc('-moz-') || myapp.checkCalc();
};

myapp.checkCalc('-webkit-'); // check webkit prefixed support
myapp.checkCalc('-moz-'); // check moz prefixed support
myapp.checkCalc(); // check unprefixed/spec support

myapp.checkAllCalc(); // or all together