Can't figure out why node won't throw in strict mode, when I modify a frozen data structure.

freeze_not_throwing.js

;(function (global) {
'use strict';
function getType (obj) {
	if (typeof obj === 'string') {
		return 'string';
	}
	else if (typeof obj === 'number') {
		return 'number';
	}
	else if (Array.isArray(obj)) {
		return 'array';
	}
	else if (obj === true || obj === false) {
		return 'boolean';
	}
	else {
		return 'object';
	}
}


function deepFreeze (obj) {
	switch (getType(obj)) {

	case 'string':
	case 'number':
	case 'boolean':
		break;

	case 'object':
		var keys = Object.keys(obj);
		var values = keys.map(function (k) {
			return obj[k];
		});
		values.map(deepFreeze);
		Object.freeze(obj);
		break;
	case 'array':
		obj.map(deepFreeze);
		Object.freeze(obj);

	}
}


var user = {
	languages: [
		'javascript',
		'python'
	],
	contact: {
		phone: '555-555-5555',
		email: '[email protected]'
	}
};

deepFreeze(user);

user.languages.push('go');

console.log(user);

})(global);