Javascript — 第04天

在JavaScript 字串是用單引號 ‘ 或雙引號 “ 包住的字。 

用單引號 ‘ 或雙引號 “ 都是一樣的，沒有特別。

更多請見 | 此好文

函式Function

function sing(song){
console.log (song)
}
sing('hey you');

也可用來計算

function multiply(a,b){
  return a;
  return a * b;
  return b;
}
multiply(5, 10);

什麼是結果呢?

只有第一個值被回傳。

在 Javascript中, 一個函式 (function)也是變數(variable)。

我們可以這麼做，如:

var a = function () {}

參數(parameters)和 引數(arguments)

更多解釋 | 見此好文

W3Shool也有playground可以參考喔

資料結構(Data Structure)

• 陣列arrays
• 物件objects

陣列Arrays

內容種類可有以下

• 字串strings
• 數字numbers
• 布林值booleans
• 函式functions
• 陣列中的陣列(??)array in array(??)

在程式語言中，0是第一個元素。

//strings
var list= ["apple", "banana", "kiwi", "melon"];
console.log(list[0]);
//numbers
var numbers = [10, 20, 30, 40];
console.log(numbers[1]);
//booleans
var booleans = [true, false, true, true, false];
console.log(booleans[2]);
//function
var functionList = [function apple(){
  console.log("apple");
}]
functionList

在Javascript中，註解comment是 //

var list = [
["bunny", "kitten", "puppy", "duckey"]
];
console.log(list[0]);

物件Objects

var user = {
  name: "John",
  age: 34,
  hobby: "soccer",
  isMarried: false,
}
user.name
user.age
user.hobby
user.isMarried
var user = {
  name: "John",
  age: 34,
  hobby: "soccer",
  isMarried: false,
  favoriuteGames: ["Hollow Knight", "League of Legends", "Horizon"],
motto: function() {
      console.log("Thats's awesome!");
  }
}
var list = [
  {
     username: "Bob",
     password: "corn"
  },
  {
     username: "Nuby",
     password: "newbie"
  }
];

var user = {
  name: "John",
  age: 34,
  hobby: "soccer",
  isMarried: false,
  favoriuteGames: ["Hollow Knight", "League of Legends", "Horizon"],
motto: function() {
      console.log("Thats's awesome!");
  }
}
var list = [
  {
     username: "Bob",
     password: "corn"
  },
  {
     username: "Nuby",
     password: "newbie"
  }
];

Null

var emptyObj = {}
var nullObj = null;
emptyObj
nullObj
nullObj.name = "Ann";
emptyObj.name = "Ann";

迴圈Loops

for / while / do while

//for loop
var todos = [
    "a",
    "b",
    "c",
    "d"
];
var todoLength = todos.length;
for (var i=0; i < todoLength; i++) {
    todos.pop();
}
//while loop
var counterOne = 10;
while( counterOne > 10) {
    console.log("while", counterOne);
    counterOne--;
}
//do-while loop
var counterTwo = 10;
do {
    console.log("do while", counterTwo);
    counterTwo--;
} while(counterTwo > 0);

While 和 do-while 的差異

其中一個沒有值，另一個先跑一次，才注意到條件而停止。

//for loop
var todos = [
    "a",
    "b",
    "c",
    "d"
];
var todoLength = todos.length;
for (var i=0; i < todoLength; i++) {
    console.log(todos[i]);
}
todos.forEach(function(todo, i) {
    console.log(todo, i);
})

//for loop
var todos = [
    "a",
    "b",
    "c",
    "d"
];
var todoMore = [
    "a",
    "b",
    "c",
    "d"
];
var todoLength = todos.length;
function logTodos(todo, i) {
    console.log(todo, i);
}
todos.forEach(function(todo, i) {
    console.log(todo, i);
})

建個Facebook

var database = [
  {
    username: "A",
    password: "1111"
  },
  {
    username: "B",
    password: "2222"
  },
  {
    username: "C",
    password: "3333"
  }
];
var newsfeed = [
  {
    username: "D",
    password: "Sunday here."
  },
  {
    username: "E",
    password: "It's Monday!"
  },
];
function isUserValid(username, password) {
    for(var i=0; i < database.length; i++) {
      if(database[i].username === username &&
         database[i].password === password) {
            return true;
      }
    }
return false;
}
function signIn(username, password) {
    if(isUserValid(username, password)) {
        console.log(newsfeed);
    } else {
          alert("Sorry, wrong username and password!");
    }
}
var usernamePrompt = prompt("What\'s your name?");
var passwordPrompt = prompt("What\'s your password?");
signIn(usernamePrompt, passwordPrompt);