Demonstrating that `~arr.indexOf(key)` is actually faster than `lookup[key]`

speed-test.js

// paste me into the console
var ALLOWED_KEYS = [
	'acorn',
	'banner',
	'cache',
	'context',
	'dest',
	'entry',
	'exports',
	'external',
	'footer',
	'format',
	'globals',
	'indent',
	'intro',
	'moduleId',
	'moduleName',
	'noConflict',
	'onwarn',
	'outro',
	'paths',
	'plugins',
	'preferConst',
	'sourceMap',
	'sourceMapFile',
	'targets',
	'treeshake',
	'useStrict'
];

function validateKeysWithArray ( object, allowedKeys ) {
	var actualKeys = keys( object );

	var i = actualKeys.length;

	while ( i-- ) {
		var key = actualKeys[i];

		if ( allowedKeys.indexOf( key ) === -1 ) {
			return new Error(
				`Unexpected key '${ key }' found, expected one of: ${ allowedKeys.join( ', ' ) }`
			);
		}
	}
}

function arrayToMap(list) {
	return list.reduce((accum, el) => {
		accum[el] = el
		return accum
	}, {})
}

 function validateKeysWithMap ( object, allowedKeys ) {
	var actualKeys = keys( object );

	var keysMap = arrayToMap(allowedKeys);
	var i = actualKeys.length;

	while ( i-- ) {
		var key = actualKeys[i];

		if (  !keysMap[key] ) {
			return new Error(
				`Unexpected key '${ key }' found, expected one of: ${ allowedKeys.join( ', ' ) }`
			);
		}
	}
}

console.time( 'validateKeysWithArray' );
validateKeysWithArray({
	entry: 'src/index.js',
	dest: 'bundle.js',
	format: 'cjs'
}, ALLOWED_KEYS );
console.timeEnd( 'validateKeysWithArray' );

console.time( 'validateKeysWithMap' );
validateKeysWithMap({
	entry: 'src/index.js',
	dest: 'bundle.js',
	format: 'cjs'
}, ALLOWED_KEYS );
console.timeEnd( 'validateKeysWithMap' );

console.time( 'validateKeysWithArray 10000 times' );
var i = 10000;
while ( i-- ) {
	validateKeysWithArray({
		entry: 'src/index.js',
		dest: 'bundle.js',
		format: 'cjs'
	}, ALLOWED_KEYS );
}
console.timeEnd( 'validateKeysWithArray 10000 times' );

console.time( 'validateKeysWithMap 10000 times' );
var i = 10000;
while ( i-- ) {
	validateKeysWithMap({
		entry: 'src/index.js',
		dest: 'bundle.js',
		format: 'cjs'
	}, ALLOWED_KEYS );
}
console.timeEnd( 'validateKeysWithMap 10000 times' );



 function validateKeysWithCachedMap ( object, allowedKeys, keysMap ) {
	var actualKeys = keys( object );

	var i = actualKeys.length;

	while ( i-- ) {
		var key = actualKeys[i];

		if (  !keysMap[key] ) {
			return new Error(
				`Unexpected key '${ key }' found, expected one of: ${ allowedKeys.join( ', ' ) }`
			);
		}
	}
}

console.time( 'validateKeysWithCachedMap 10000 times' );
var cachedMap = arrayToMap(ALLOWED_KEYS);
var i = 10000;
while ( i-- ) {
	validateKeysWithCachedMap({
		entry: 'src/index.js',
		dest: 'bundle.js',
		format: 'cjs'
	}, ALLOWED_KEYS, cachedMap );
}
console.timeEnd( 'validateKeysWithCachedMap 10000 times' );