var bNoParam = new Boolean();
var bZero = new Boolean(0);
var bNull = new Boolean(null);
var bEmptyString = new Boolean('');
var bfalse = new Boolean(false);
下面boolean对象的初始值都是true：
var btrue = new Boolean(true);
var btrueString = new Boolean('true');
var bfalseString = new Boolean('false');
var bSuLin = new Boolean('Su Lin');
var bArrayProto = new Boolean([]);
var bObjProto = new Boolean({});
var x = 10;
function createFunction1() {
var x = 20;
return new Function('return x;'); // this |x| refers global |x|
}
function createFunction2() {
var x = 20;
function f() {
return x; // this |x| refers local |x| above
}
return f;
}
var f1 = createFunction1();
console.log(f1()); // 10
var f2 = createFunction2();
console.log(f2()); // 20
Date
Date是js中用来操作时间的Object。我们看下Date的常用例子：
let today = new Date()
let birthday = new Date('December 17, 1995 03:24:00')
let birthday = new Date('1995-12-17T03:24:00')
let birthday = new Date(1995, 11, 17) // the month is 0-indexed
let birthday = new Date(1995, 11, 17, 3, 24, 0)
let birthday = new Date(628021800000) // passing epoch timestamp
let [month, date, year] = ( new Date() ).toLocaleDateString().split("/")
let [hour, minute, second] = ( new Date() ).toLocaleTimeString().slice(0,7).split(":")
Array
JS内置了很多种不同类型的Array，最常用的就是Array字面量和Array Object。
我们看下怎么创建一个Array：
let fruits = ['Apple', 'Banana'];
console.log(fruits.length); // 2
console.log(fruits[0]); // "Apple"
let fruits = new Array('Apple', 'Banana');
console.log(fruits.length); // 2
console.log(fruits[0]); // "Apple"
遍历Array：
let fruits = ['Apple', 'Banana']
fruits.forEach(function(item, index, array) {
console.log(item, index)
})
// Apple 0
// Banana 1
添加Item到Array：
let newLength = fruits.push('Orange')
// ["Apple", "Banana", "Orange"]
从最后删除item：
let last = fruits.pop() // remove Orange (from the end)
// ["Apple", "Banana"]
从前面删除item：
let first = fruits.shift() // remove Apple from the front
// ["Banana"]
从前面添加item：
let newLength = fruits.unshift('Strawberry') // add to the front
// ["Strawberry", "Banana"]
删除某个index的item：
let removedItem = fruits.splice(pos, 1) // this is how to remove an item
// ["Strawberry", "Mango"]
删除多个item：
let vegetables = ['Cabbage', 'Turnip', 'Radish', 'Carrot']
console.log(vegetables)
// ["Cabbage", "Turnip", "Radish", "Carrot"]
let pos = 1
let n = 2
let removedItems = vegetables.splice(pos, n)
// this is how to remove items, n defines the number of items to be removed,
// starting at the index position specified by pos and progressing toward the end of array.
console.log(vegetables)
// ["Cabbage", "Carrot"] (the original array is changed)
console.log(removedItems)
// ["Turnip", "Radish"]
拷贝array：
let shallowCopy = fruits.slice() // this is how to make a copy
// ["Strawberry", "Mango"]
let contacts = new Map()
contacts.set('Jessie', {phone: "213-555-1234", address: "123 N 1st Ave"})
contacts.has('Jessie') // true
contacts.get('Hilary') // undefined
contacts.set('Hilary', {phone: "617-555-4321", address: "321 S 2nd St"})
contacts.get('Jessie') // {phone: "213-555-1234", address: "123 N 1st Ave"}
contacts.delete('Raymond') // false
contacts.delete('Jessie') // true
console.log(contacts.size) // 1
遍历Map：
let myMap = new Map()
myMap.set(0, 'zero')
myMap.set(1, 'one')
for (let [key, value] of myMap) {
console.log(key + ' = ' + value)
}
// 0 = zero
// 1 = one
for (let key of myMap.keys()) {
console.log(key)
}
// 0
// 1
for (let value of myMap.values()) {
console.log(value)
}
// zero
// one
for (let [key, value] of myMap.entries()) {
console.log(key + ' = ' + value)
}
// 0 = zero
// 1 = one
使用forEach来遍历map：
myMap.forEach(function(value, key) {
console.log(key + ' = ' + value)
})
// 0 = zero
// 1 = one
Set中存储的是唯一的对象。
我们看下Set的操作：
let mySet = new Set()
mySet.add(1) // Set [ 1 ]
mySet.add(5) // Set [ 1, 5 ]
mySet.has(1) // true
mySet.delete(1) // removes 1 from the set
set的遍历：
// logs the items in the order: 1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}
for (let item of mySet) console.log(item)