function main() {
    console.log("Hello World!");
}
main()
var main = function() {
    console.log("Hello World!2");
}
main()

/* ========================================================================== */
/*                                  if else:                                  */
/* ========================================================================== */

var a = 5 > 4 ? 'yes' : 'no';
var b = 10 == '100' ? 'yes': 'no';
console.log(b, 'aaah', a)


main(85)
main(44)
main(98)

function main(grade) {
    if (grade < 60) {
        console.log('F');
    } else if (grade < 70) {
        console.log('D');
    } else if (grade < 80) {
        console.log('C');
    } else if (grade < 90) {
        console.log('B');
    } else  console.log('A');
}

 /* ========================================================================== */
 /*                                 for loops;                                 */
 /* ========================================================================== */

for (let i = 0; i < 10; i++ ) {  // for (assign, while, function apply)
    console.log(i);
}

for (let i = 100; i >= 0; i-=5 ) {
    console.log(i);
}

var data = [3, 7, 2, 9, 1, 11];
var sum = 0;
data.forEach(function(d){
    sum += d;
    console.log(sum);
});

var t = "Hello World";
for (let c of t) {
    console.log(c);
}



var i=0
console.log('yes', i++<4, i, '\n') // i++ ==> i = i+1
while (i<5, i++<4) {
    i += 2
    console.log(i)
}


var i=0
var q="a string that cool"
do{
    i++
    console.log(q.charAt(2),  m = q.split(/\s/)) 
    for (let b = 0; (b<=1) | (b < m.length); b++) {
        console.log(m[b])
    }
}while(i<1)

let c ={id: 9, type: "f"}
// c to f temperature.
function main(){
    var fahr;
    // console.log(c.id);
    fahr = prompt("Enter the temperature in F: ");
    const ratio = 5.0/9.0;
    let cel = (fahr - 32) * ratio;
    writeln("The temperature in C is: " + cel);
}

main()



function removeVowels(s) {
    const vowels = "aeiouAEIOU";
    let sWithoutVowels = "";
    for (let eachChar of s) {
        // console.log(s, '===', eachChar, '===', vowels.indexOf(eachChar))
        if (vowels.indexOf(eachChar) === -1) {
            sWithoutVowels = sWithoutVowels + eachChar
        }
    }
    return sWithoutVowels
}

console.log(removeVowels("asjdiajisjd1ijinfss"))


// array & set.

var s = new String('0');
console.log(s??false);
console.log(s);


var arr = []
console.log(arr instanceof Array, Array.isArray(arr))

var set = new Set([1, 2]) 
console.log(typeof set, typeof Array.from(set))
console.log(Array.from(set))

/* ========================================================================== */
/*                                    数组去重:                                */
/* ========================================================================== */
var arr = [1, 2, 2, 4, 9, 6, 7, 5, 2, 3, 5, 6, 5]
// console.log(Array.from(new Set(arr))) 
console.log(arr, '\n',(new Set(arr))) 
console.log(Array.from(new Set(arr))) 
// set() 就可以去重

//2. write a function;

var arr = [1, 2, 2, 4, 9, 6, 7, 5, 2, 3, 5, 6, 5]
function gunique1(arr){
    let newArr = [-1]
    let arrsort= arr.sort()
    for (let i=0; i<arr.length; i++){
        if (arrsort[i] > newArr[newArr.length - 1]){
            newArr.push(arrsort[i])
            // console.log(arrsort[i], newArr[newArr.length - 1], arrsort[i] > newArr[newArr.length - 1])
        }
    }
    newArr.shift() // removes the first element of an array
    return console.log(newArr)
};

gunique1(arr)

//
var arr = [1, 2, 2, 4, 9, 6, 7, 5, 2, 3, 5, 6, 5]
function unique(arr) {
    arr.sort()
    let newArr = [arr[0]]
    for (let i = 0; i < arr.length; i++) {
        let item = arr[i] // item = 0 now.
        if (newArr[newArr.length - 1] !== item) {
            newArr.push(item)
        }
    }
    return newArr
}
unique(arr)

// flatten array
var arr = [1, 2, [3, [4, 5]]]
console.log(arr.flat(Infinity))


var arr = [1, 2, [3, [4, 5]]]
function flat(arr) {
    let str = JSON.stringify(arr).replace(/[\[|\]]/g, '')
    str = `[${str}]`
    return JSON.parse(str)
}
console.log(flat(arr))



/* ========================================================================== */
/*                            arrow functions in js                           */
/* ========================================================================== */
var materials = [
    'Hydrogen',
    'Helium',
    'Lithium',
    'Beryllium'
];

console.log(materials.map(material => material.length));
// expected output: Array [8, 6, 7, 9]


(function (a) {
    return console.log(a + 100);
})(3)

// (a) => {
//     return console.log(a + 100);
// }; //easier version. a => a + 100;


var materials = [
    'Hydrogen',
    'Helium',
    'Lithium',
    'Beryllium'
];
var b = ['sda','asda','asd', 'bsdf'] 
b.map((a,b)=>console.log(a+b+'aaaa')) // arrow function second element is index.

// sort arr

var arr = [2, 7, 0, 6, 1, 4, 8, 3]
console.log((arr) instanceof Array, typeof arr)
console.log(arr.sort())
console.log(arr.sort().reverse())
console.log("==========================================================================")
console.log(arr.sort((a, b) => a - b)) // 递增
console.log(arr.sort((a, b) => b - a)) // 递减
console.log(arr.sort((a, b) => b - a > 0)) // 递减 这个hide了一个条件.


/* ========================================================================== */
/*                                    class                                   */
/* ========================================================================== */

function Animal(name, size) {
    this.name = name
    this.size = size
}

Animal.prototype.eat = function (food) {
    console.log(this.name + "is eating " + food, "and " + this.name +' is getting fatter of ' + this.size)
}

var ani = new Animal('xiaoyou', '15 kilo') 
ani.eat('banana')
// xiaoyouis eating banana and xiaoyou is getting fatter of 15 kilo

class Rectangle {
    constructor(height, width) {
        this.height = height;
        this.width = width;
    }
    // Getter
    get area() {
        return this.calcArea();
    }
    // Method
    calcArea() {
      return this.height * this.width;
    }

    calcVolume(length){
        return this.height * this.width * length;
    }
}
const square = new Rectangle(10, 10);
console.log(square.area); // 100
console.log(square.calcVolume(22)); // 2200


console.log(Array(9).length)

var a = (Array(9).fill(null))
var k = (a.length===1 ? '91':'hahhah')
console.log(k)


// \\ operatopr()

let x = 3;
var z = ++x;
var y = x++;

console.log(`x:${x}, y:${y}, z:${z}`);
// expected output: "x:4, y:3"


const car = { make: 'Honda', model: 'Accord', year: 1998 };
console.log('make' in car);
delete car.make;
if ('make' in car === false && 'model' in car !== true) {
    car.make = 'Suzuki';
} else if ('model' in car ) {
    car.make = 'Benz';
};
console.log(car.make);
//\\




function haha(x){
    if (x){
        console.log('x is valid')
    }else{
        console.log('empty passed')
    };
    return;
}
q = haha()
if(q == null){console.log('returned undefined aka null')}