deadunitCore.browser.umd.js
function(e) {
	        if (e['arguments'] && e.stack) {
	            return 'chrome';
	        } else if (e.stack && e.sourceURL) {
	            return 'safari';
	        } else if (e.stack && e.number) {
	            return 'ie';
	        } else if (typeof e.message === 'string' && typeof window !== 'undefined' && window.opera) {
	            // e.message.indexOf("Backtrace:") > -1 -> opera
	            // !e.stacktrace -> opera
	            if (!e.stacktrace) {
	                return 'opera9'; // use e.message
	            }
	            // 'opera#sourceloc' in e -> opera9, opera10a
	            if (e.message.indexOf('\n') > -1 && e.message.split('\n').length > e.stacktrace.split('\n').length) {
	                return 'opera9'; // use e.message
	            }
	            // e.stacktrace && !e.stack -> opera10a
	            if (!e.stack) {
	                return 'opera10a'; // use e.stacktrace
	            }
	            // e.stacktrace && e.stack -> opera10b
	            if (e.stacktrace.indexOf("called from line") < 0) {
	                return 'opera10b'; // use e.stacktrace, format differs from 'opera10a'
	            }
	            // e.stacktrace && e.stack -> opera11
	            return 'opera11'; // use e.stacktrace, format differs from 'opera10a', 'opera10b'
	        } else if (e.stack && !e.fileName) {
	            // Chrome 27 does not have e.arguments as earlier versions,
	            // but still does not have e.fileName as Firefox
	            return 'chrome';
	        } else if (e.stack) {
	            return 'firefox';
	        }
	        return 'other';
	    }
function(e) {
	        if (e['arguments'] && e.stack) {
	            return 'chrome';
	        } else if (e.stack && e.sourceURL) {
	            return 'safari';
	        } else if (e.stack && e.number) {
	            return 'ie';
	        } else if (typeof e.message === 'string' && typeof window !== 'undefined' && window.opera) {
	            // e.message.indexOf("Backtrace:") > -1 -> opera
	            // !e.stacktrace -> opera
	            if (!e.stacktrace) {
	                return 'opera9'; // use e.message
	            }
	            // 'opera#sourceloc' in e -> opera9, opera10a
	            if (e.message.indexOf('\n') > -1 && e.message.split('\n').length > e.stacktrace.split('\n').length) {
	                return 'opera9'; // use e.message
	            }
	            // e.stacktrace && !e.stack -> opera10a
	            if (!e.stack) {
	                return 'opera10a'; // use e.stacktrace
	            }
	            // e.stacktrace && e.stack -> opera10b
	            if (e.stacktrace.indexOf("called from line") < 0) {
	                return 'opera10b'; // use e.stacktrace, format differs from 'opera10a'
	            }
	            // e.stacktrace && e.stack -> opera11
	            return 'opera11'; // use e.stacktrace, format differs from 'opera10a', 'opera10b'
	        } else if (e.stack && !e.fileName) {
	            // Chrome 27 does not have e.arguments as earlier versions,
	            // but still does not have e.fileName as Firefox
	            return 'chrome';
	        } else if (e.stack) {
	            return 'firefox';
	        }
	        return 'other';
	    }
Mode could differ for different exception, e.g.
exceptions in Chrome may or may not have arguments or stack.

@return {String} mode of operation for the exception