If...Else Statements

if 跟 else 後面的判斷不用加分號，分號在後面。

if (12 >= 10)
{console.log("You got a true!");
} else {
console.log("You got a false!");
}

詢問年齡，判別後做回應

var age = prompt("What's your age");

if(age < 13)
{console.log("they're allowed to play but you take no responsibility.");
}
else
{console.log("Don't give up");
}

Using console.log()

Prints into the console whatever we put in the parentheses.

For debugging purposes, you can use the console.log() method to display data.

console.log()
prompt("when can i sleep?")

//會跳出對話框

計算餘數

console.log(14%3)

Substrings

指定字串中其中幾個字

"hello". substring(0, 2);

以上面的程式碼為例，把hello拆成0~4
要記得第一個字排序是0

0 1 2 3 4

| | | | |

h e l l o

使用 console.log 顯示結果

console.log("January".substring(0,3))

設置變數

var myAge = 26;
console.log(myAge);

So the variable stores the value of the variable, whether that is a number or a string
We store data values in variables. We can bring back the values of these variables by typing the variable name.
變數的第一個字必須是小寫(lowercase letter)

Variable Scope

Scope can be global or local
差別在一個變數在 function 外定義，一個在 function 內

Global Variable

Variables defined outside a function are accessible anywhere once they have been declared. They are called global variables and their scope is global.

For Example

var globalVar = "hello";

var foo = function() {
console.log(globalVar);
prints "hello"
}

Local Variable

變數定義在 function 內

var bar = function() {
var localVar = "howdy";
}

console.log(localVar);
error

Global variable 和 Local variable

在第四行中加入 var 造成 function 內的 my_number 變成local variable，第一行變成global variable

var my_number = 7; //this has global scope

var timesTwo = function(number) {
var my_number = number * 2;
console.log("Inside the function my_number is: ");
console.log(my_number);
};

timesTwo(7);
console.log("Outside the function my_number is: ")
console.log(my_number);

Manipulating numbers & strings

comparisons (e.g. >, <=)
modulo (e.g. %)

Function syntax

var greeting = function (name) {
console.log("Great to see you," + "" + name);
};

greeting("Jeffrey");

1.Declaring a function using var

2.The name of function should begin with lowercase letter

3.The code in the parentheses is called a parameter

function後設定此function的參數(parameter)

4.The entire function ends with a semi-colon.

5.呼叫function時，we call the function by just typing the function's name and putting a parameter value inside parentheses after it

多於一個 parameter 的 function

var perimeterBox =function(length,width){
return length + length + width + width;
}

perimeterBox(5,5)

String Concatenation

把字串連起來(concatenation)，如果你要字與字之間有空格，要記得加進空格，如下：

console.log("Hey" + " " + "you");

Return

When we call a function, its return value is just the result from running the function.

var quarter = function(number){
return number/4;
}

HTML的註解

使用將要註解的文字包起來。

<!--我是註解 -->

CSS的註解

使用/* 與 */ 將要註解的文字包起來。

<STYLE>

/*這裡是註解*/

.樣式名a{
CSS屬性名A:屬性值;
CSS屬性名B:屬性值;
}

.樣式名b{
CSS屬性名B:屬性值;
CSS屬性名C:屬性值;
/*CSS屬性名D:屬性值; 這個屬性暫時不用*/
}

</STYLE>

JavaScript 的註解

JavaScript 的註解符號和 Java 一樣，

註解的方式有兩種：

（1）/* */ 多行的註解

（2）// 單行註解

單行註解是從到該行結尾

/*
多行註解可以橫跨多行
但是在註解中不可以再打一次註解
*/

Java 的註解

陣列的介紹 Arrays

Any time you see data surrounded by [ ], it is an array.
Store lists of data
Can store different data types at the same time
Are ordered so the position of each piece of data is fixed

Examples:

var names = ["Mao","Gandhi","Mandela"];
var sizes = [4, 6, 3, 2, 1, 9];
var mixed = [34, "candy", "blue", 11];

Array positions

陣列中第一個值的 indexing number 是 0
Arrays have 0-based indexing, so we start counting the positions from 0.
假設現在有一個 array

var arrayName = ["Mao","Gandhi","Mandela"];

arrayName[0] 代表陣列中的第一個值 Mao，arrayName[1] 代表陣列中的第二個值 Gandhi，以此類推

應用案例

var cities = ["Melbourne", "Amman", "Helsinki", "NYC","Taipei"];

for (var i = 0; i < cities.length; i++) {

console.log("I would like to visit " + cities[i]);

}

console.log(cities.length)

避免text過長，可以使用backslash

var text = "Hey, how are you \
doing? My name is Emily.";

字串也可以用陣列呼叫

var myName = 'Eric';

myName[0]; equals 'E'

簡潔的 code, less is more

var bool = true;

while(bool){
Do something
}

等同於

var bool = true;

while(bool === true){
Do something
}

JavaScript