提高代码效率：充分利用JS的内置对象

var numbers = [1, 2, 3, 4, 5];
numbers.forEach(function(number) {
    console.log(number * 2);
});

var numbers = [1, 2, 3, 4, 5];
var doubleNumbers = numbers.map(function(number) {
    return number * 2;
});
console.log(doubleNumbers);

var numbers = [1, 2, 3, 4, 5];
var oddNumbers = numbers.filter(function(number) {
    return number % 2 !== 0;
});
console.log(oddNumbers);

var person = {
    name: 'John',
    age: 30,
    gender: 'male'
};
var keys = Object.keys(person);
console.log(keys);

var person = {
    name: 'John',
    age: 30,
    gender: 'male'
};
var values = Object.values(person);
console.log(values);

var person1 = {
    name: 'John',
    age: 30
};
var person2 = {
    gender: 'male'
};
var mergedPerson = Object.assign({}, person1, person2);
console.log(mergedPerson);

var sentence = 'Hello, world!';
var position = sentence.indexOf('world');
console.log(position);

var sentence = 'Hello, world!';
var words = sentence.split(',');
console.log(words);

var sentence = 'Hello, world!';
var newSentence = sentence.replace('world', 'JavaScript');
console.log(newSentence);