JAVAScript的数据类型在大的方向上分为两类：1）primitive types and 2）object tyeps。

其一 primitive types包括常规的 numbers，string， booleans 以及特殊类型的 null 和 undefined。而且以上五类都是immutuable types；

其二，object types 包括object，以及特殊类型的object即array。其他比如 Set，Map，typed array, RegExp and Date types.

一、Numbers

Numeric literal 表示 十六进制，二进制和八进制：

//integer literals
> 0xff
255
> 0b1011
11
> 0o377
255
> 377
377
//floating-point literals
undefined
> 6.02e23
6.02e+23
> 1.47e-23
1.47e-23
//Arithmetic 
Math.hypo

//Infinity
Infinity                    // A positive number too big to represent
Number.POSITIVE_INFINITY    // Same value
1/0                         // => Infinity
Number.MAX_VALUE * 2        // => Infinity; overflow

-Infinity                   // A negative number too big to represent
Number.NEGATIVE_INFINITY    // The same value
-1/0                        // => -Infinity
-Number.MAX_VALUE * 2       // => -Infinity

NaN                         // The not-a-number value
Number.NaN                  // The same value, written another way
0/0                         // => NaN
Infinity/Infinity           // => NaN

Number.MIN_VALUE/2          // => 0: underflow
-Number.MIN_VALUE/2         // => -0: negative zero
-1/Infinity                 // -> -0: also negative 0
-0

// The following Number properties are defined in ES6
Number.parseInt()       // Same as the global parseInt() function
Number.parseFloat()     // Same as the global parseFloat() function
Number.isNaN(x)         // Is x the NaN value?
Number.isFinite(x)      // Is x a number and finite?
Number.isInteger(x)     // Is x an integer?
Number.isSafeInteger(x) // Is x an integer -(2**53) < x < 2**53?
Number.MIN_SAFE_INTEGER // => -(2**53 - 1)
Number.MAX_SAFE_INTEGER // => 2**53 - 1
Number.EPSILON          // => 2**-52: smallest difference between numbers
// 浮点数 
18,437,736,874,454,810,627 只有这么多浮点数，能被表示出来。
// rouding problems 
//BigInt

//Date and time
let timestamp = Date.now();  // The current time as a timestamp (a number).
let now = new Date();        // The current time as a Date object.
let ms = now.getTime();      // Convert to a millisecond timestamp.
let iso = now.toISOString(); // Convert to a string in standard format.

二、String and Text

// 1.string literals
// 2.escape sequences 
// 3.string methods
// 4.template literals (tagged template literals)
// 5.Pattern Matching 
/[1-9][0-9]*/; 

三、Boolean Values

只有 true 和 false 这两项。

四、null and undefined

> typeof(null)
'object'

五、Symbols

let s = Symbol.for("shared");
let t = Symbol.for("shared");
s === t          // => true
s.toString()     // => "Symbol(shared)"
Symbol.keyFor(t) // => "shared"

六、Global

• Global constants like undefined, Infinity, and NaN
• Global functions like isNaN(), parseInt() (§3.9.2), and eval() (§4.12)
• Constructor functions like Date(), RegExp(), String(), Object(), and Array() (§3.9.2)
• Global objects like Math and JSON (§6.8)

七、Immutable Primitives and Mutable Object Referece

> function equalArray(a, b) {
... if (a === b) return true;
... if (a.length !== b.length) return false;
... for (let i = 0; i < a.length; i++) {
..... if (a[i] !== b[i]) return false;
..... }
... return true;
... }

八、Type Conversions

implicite conversion and explicite conversions

九、Variable Declaration and Assignment

// Destructuring Assignment
[x,y] = [x+1,y+1];  // Same as x = x + 1, y = y + 1
[x,y] = [y,x];      // Swap the value of the two variables
// Same as const sin=Math.sin, cos=Math.cos, tan=Math.tan
const {sin, cos, tan} = Math;
//此处与Python的用法完全一致。