This project very good, so I use it in many of my projects, so I recommend the following suggestions here:

• Multiple file processing
• Preferred quote style for strings -- I very like use double quotes ^_^
• When we turn on String Array, our array can consider using a single Unicode Escape Sequence. The remaining strings can be considered separately.
• Substitute void 0 if there is a variable named undefined in scope (variable name will be mangled, typically reduced to a single character)

An example of a combination of obfuscate() options:

var SourceCodeList = {
    "test_1.js": "function hi(){console.log(\"Hello World!\");}hi();",
    "test_2.js": "console.log(\"Welcome use a free and efficient obfuscator for JavaScript\");"
};
var options = {
	compact: true,
	controlFlowFlattening: true,
	controlFlowFlatteningThreshold: 0.75,
	deadCodeInjection: true,
	deadCodeInjectionThreshold: 0.4,
	debugProtection: false,
	debugProtectionInterval: false,
	disableConsoleOutput: true,
	identifierNamesGenerator: 'hexadecimal',
	renameGlobals: false,
	rotateStringArray: true,
	selfDefending: true,
	shuffleStringArray: true,
	splitStrings: true,
	splitStringsChunkLength: '10',
	stringArray: true,
	stringArrayEncoding: 'base64',
	stringArrayThreshold: 0.75,
	transformObjectKeys: true,
	unicodeEscapeSequence: false
};
var obfuscationResult = JavaScriptObfuscator.obfuscate(SourceCodeList, options);
console.log(obfuscationResult.getObfuscatedCode());

Third point comparison

Before:

var _0x2e7f=['Hello\x20World!','log'];(function(_0x53d6b3,_0x2e7f7e){var _0x41301a=function(_0x3ed08d){while(--_0x3ed08d){_0x53d6b3['push'](_0x53d6b3['shift']());}};_0x41301a(++_0x2e7f7e);}(_0x2e7f,0x1c4));var _0x4130=function(_0x53d6b3,_0x2e7f7e){_0x53d6b3=_0x53d6b3-0x0;var _0x41301a=_0x2e7f[_0x53d6b3];return _0x41301a;};function hi(){console[_0x4130('0x1')](_0x4130('0x0'));}hi();

After:

var _0x2e7f=['\x6c\x6f\x67','\x48\x65\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21'];(function(_0x53d6b3,_0x2e7f7e){var _0x41301a=function(_0x3ed08d){while(--_0x3ed08d){_0x53d6b3['push'](_0x53d6b3['shift']());}};_0x41301a(++_0x2e7f7e);}(_0x2e7f,0x1c4));var _0x4130=function(_0x53d6b3,_0x2e7f7e){_0x53d6b3=_0x53d6b3-0x0;var _0x41301a=_0x2e7f[_0x53d6b3];return _0x41301a;};function hi(){console[_0x4130('0x1')](_0x4130('0x0'));}hi();