program Structure

BINDINGS or variables 

    keyword: let, var, const:

BINDING NAMES: 

        A binding name may include dollar signs ($) or underscores (_) but no other

    punctuation or special characters.

ENVIRONMENT:

        The collection of bindings and their values that exist at a given time is called
    the environment. When a program starts up, this environment is not empty. It
    always contains bindings that are part of the language standard, and most of the
    time, it also has bindings that provide ways to interact with the surrounding
    system. For example, in a browser, there are functions to interact with the
    currently loaded website and to read mouse and keyboard input.

FUNCTIONS:

    A function is a piece of program wrapped in a value .

Control flow :

    C类似： if whiel, do-while, for-loops, break, continue, switch-case

Functions as values

    let launchMissiles = function() {
        missileSystem.launch("now");
    }; 

    Declaration notation (没有顺序)

    function square(x) {
        return x * x;
    } 

Arrow functions

    const square1 = (x) => { return x * x; };

Optional Arguments

    function minus(a, b) {
    if (b === undefined) return -a;
        else return a - b;
    }

 Rest parameters 

 function max(...numbers) {

        let result = -Infinity;
        for (let number of numbers) {
        if (number > result) result = number;
        }
            return result;
        }
    console.log(max(4, 1, 9, -2));
    // → 9 

function power(base, exponent = 2) {

    let result = 1;
    for (let count = 0; count < exponent; count++) {
        result *= base;
    }
        return result;
    } 

Data Structures: Objects and Arrays

let anObject = {left: 1, right: 2};
console.log(anObject.left);
// → 1
delete anObject.left;
console.log(anObject.left);
// → undefined
console.log("left" in anObject);
// → false
console.log("right" in anObject);
// → true 

console.log(Object.keys({x: 0, y: 0, z: 2}));
// → ["x", "y", "z"] 

let objectA = {a: 1, b: 2};
Object.assign(objectA, {b: 3, c: 4});
console.log(objectA);
// → {a: 1, b: 3, c: 4} 

mutability:

对象的比较是对象id的比较，类似python对象 is 比较

Number , string,  boolen, 内置数据类型不可变，

let kim = "Kim";
kim.age = 88;
console.log(kim.age);
// → undefined 

DESTRUCTURE

function phi(table) {
return (table[3] * table[0] - table[2] * table[1]) /
Math.sqrt((table[2] + table[3]) *
(table[0] + table[1]) *
(table[1] + table[3]) *
(table[0] + table[2]));
} 

function phi([n00, n01, n10, n11]) {
return (n11 * n00 - n10 * n01) /
Math.sqrt((n10 + n11) * (n00 + n01) *
(n01 + n11) * (n00 + n10));
} 

JSON

JSON.stringify(object) ， JSON.parse(string)