JavaScript 常用語法

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檢查變數型別

//宣告方式
const               //constant(常數)，宣告後，值不能改變
var                 //variable(變數)，宣告後，值可以變更
let                 //variable(變數)，宣告後，值可以變更(ES6後，建議使用)

//基本型別：number、string、boolean、null、undefined
//物件型別：object、function

typeof 3.14159      //number
typeof "flystudiox" //string
typeof true         //boolean
typeof {}           //object
typeof []           //object
typeof null         //object
typeof undefined    //undefined
typeof alert        //function
typeof NaN          //number

陣列

var aircrafts = ["Rocket", "Helicopter" , "Drone"]; //陣列宣告
var first = aircrafts[0];                           //查出陣列第一個項目
var last = aircrafts[aircrafts.length - 1];         //查出陣列最後一個項目
var length = aircrafts.length;
var isArray = aircrafts.isArray();

var newLength = aircrafts.push("Fighter");          //加入項目到陣列尾端
var last = aircrafts.pop();                         //移除陣列最後一個項目
var first = aircrafts.shift();                      //移除陣列第一個項目
var newLength = aircrafts.unshift("Fighter");       //加入項目到陣列前端
var position = aircrafts.indexOf("Rocket");         //查詢項目在陣列中，為第幾項

var removedItem = aircrafts.splice(position, n);    //從position開啟，移除n個項目
var shallowCopy = aircrafts.slice();                //複製陣列

var strAircraft = aircrafts.join();                 //將陣列轉換成字串(預設用逗號分隔)
var strAircraft = aircrafts.join("\n");             //將陣列轉換成字串(用換行符號分隔)
var aryAircraft = strAircraft.split(",");           //將字串轉換成陣列(用逗號拆解)

//二維陣列
var aircrafts = [
    ["Rocket","Helicopter"],
    ["Drone","Fighter"] ];
var first = aircrafts[0][0];
 
//歷遍陣列
aircrafts.forEach(function(item, index, array) {
    console.log(item, index);
});

條件控制

if (timeZone == "Taiwan"){
  console.log("GMT+8.");
}else if(timeZone == "Japan"){
  console.log("GMT+9.");
}else{
  console.log("Unknown time zone!");
}

switch (timeZone) {
  case "Taiwan":
    console.log("GMT+8.");
    break;
  case "Japan":
    console.log("GMT+9.");
    break;
  default:
    console.log("Unknown time zone!");
    break;
}

for (var i = 1; i <= 3; i++) {
  console.log(i);
}

var i = 1;
while ( i <= 3 ){
  console.log( i );
  i++;
}

function(函式)

JSON.stringify()        //將物件轉為JSON字串
JSON.parse()            //將JSON字串轉為物件
Number.isNaN()          //檢查是否為數字型態
Array.isArray()         //檢查是否為陣列型態
String.replace("A","B") //將A取代為B

function timeZone(area) {
  return "This area time zone is ...";
}

var timeZone = function (area) {
  return "This area time zone is ...";
};

var timeZone = new Function("string", "return 'This area time zone is ...'");

confirm

var IsConfirm = confirm("是否確定送出?");
if (!IsConfirm) { return false; }

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