JavaScriptのメモ

変数

let price = 200;//ブロック変数
const tax = 10;//定数
var fruit = "apple:orange:banana";
var fruit = new Array();
var fruit = new Array(3);
var fruit = new Array("apple","orange","banana");
var fruit = ["apple","orange","banana"];
var fruit_obj = {
    "name": "apple",
    "price": 200
};

オブジェクト

var obj = [
{
    name : 'Apple',
    purchase : 30,
    area : [{addr: '東京', price: 100},
            {addr: '大阪', price: 110}]
},
{
    name : 'Orange',
    purchase : 40,
    area : [{addr: '東京', price: 200},
            {addr: '大阪', price: 190}]
}
];

Object.keys(obj[0]);//name,purchase,area
obj[0].area[0].price;//100
'area2' in obj[0];//false
obj[0].hasOwnProperty('name');//true
obj[0]['name'];//true

//var_dumpっぽい関数 function var_dump_obj(obj, level = 0) { var ret = ''; for (var key in obj) { for (var level_count = 0; level_count < level; level_count++) { ret += '    '; } var objtype = toString.call(obj[key]).slice(8, -1).toLowerCase(); if (objtype == 'object' || objtype == 'array') { ret += '[' + key + ']' + '<br>'; ret += var_dump_obj(obj[key], level + 1); } else if (objtype == 'string') { ret += key + ': "' + obj[key] + '"<br>'; } else { ret += key + ': ' + obj[key] + '<br>'; } } return(ret); }

文字列

fruit.length;
fruit.substring(6, 11);
fruit.substr(6, 6);
fruit = str.split(":");
fruit.replace("apple", "melon");
fruit.indexOf("banana", 10);

基本構文

alert(name[0]); 
if (price < 100) {
} else if (price < 200) {
} else {
}
while (count <= 10) {
}
do {
  count++;
} while (count < 10);
for (var i = 1; i <= 10; i++) {
    break;
}
for (var fruit_data in fruit) {
}
function disp_price(id) {
}

// == の反対が !== で === の反対が !=== と思われがち
if(name == "apple"){
}else if(name === "banana"){
}else if(name != "orange"){
}else if(name !== "melon"){
}
//JavaScriptでは < の位置は固定なので =< とか => は使えない
//アロー関数に => を取られたのが原因っぽい
if(price <= 100){
}else if(price >= 1000){
}

fruit.unshift("melon");
fruit.push("melon");
fruit.shift();
fruit.pop();
fruit.sort();
fruit3 = fruit.concat(fruit2);

try {
} catch (e) {
} finally {
}

Math.floor(Math.random() * 6) + 1;
Math.floor(10.5);

date = new Date(2021, 7, 1, 23, 59, 59);
date = new Date();
date = new Date('2021/7/1 23:59:59');
date.getTime();

桜の扉