Null.ly

var 変数名;  // 宣言
変数名 = 値;  // 代入

var 変数名 = 値; // 宣言と代入を同時に

var score = 10;

var a = 10,
    b = 100,
    c = 1000;

var 123abc = 'test'; // NG

// 一行コメント

/* 複数行に
   またがる
   コメント */

// 次の行は無視される
// var a = 10;

var num1 = 10,
    num2 = 10.5,
    num3 = 1034;

var hex = 0xFF; // 255

var a = parseInt('32', 10);    // 32
var b = parseFloat('10.5');     // 10.5

var greeting1 = 'hello world',
    greeting2 = "hello world";
    
var genre = 'Rock\'n Roll'; // Rock'n Roll
var tag = "<div class=\"cleafix\"></div>";  // <div class="clearfix"></div>

var str = String(10);  // "10"

var like = true,
    hate = false;

var success = Boolean(1);  // true

var pattern = /java(script)?/gi;

pattern.test('Java');   // true
pattern.test('JavaScript'); // true
pattern.test('Objective-C');    // false

var regexp = RegExp("Go{2,3}gle"); // /Go{2,3}gle/

var foo = null;

undefined = void 0; // 確実に undefined を得る方法

var obj = { a: 10, b: 20, hello: 'world' };
var val1 = obj.a; // 10

var arr = [10, 20, 30, 'Hello', 'world'];
var val = arr[0]; // 10
var len = arr.length; // 5

arr.push(100);
arr.push(200);

// arr is [10, 20, 30, 'Hello', 'world', 100, 200]

len = arr.length // 7

function funcName() {
    // do something...
}

var a = 10 + 20; // 30

var a = 10 - 20; // -10

var a = 10 * 20; // 200

var a = 10 / 20; // 0.5

var a = 5 % 3; // 2

var a = 0;
a++;  // 1
a++;  // 2

var a = 100;
a--;  // 99
a--;  // 98

var a = 10;
a += 100;  // 110 (a = a + 100; と同様)
a -= 50;  // 60 (a = a - 50; と同様)

a == b;     // 一致
a === b;    // 完全に一致
a != b;     // 一致しない
a > b;       // a は b より大きい
a >= b;      // a は b より大きいか等しい
a < b;       // a は b 未満
a <= b;      // a は b 以下

'10' == 10      // true
'10' === 10     // false

var message = 'hello';
message = message + ', world.'; // 'hello, world.'
message += ' everyone!'; // 'hello, world. everyone!'

var a = true, b = false, c = true, d = false;

a && b;  // false
a && c;  // true

a || b;  // true
b || d;  // false

!(a && b);  // true
!(b || d);  // true

var child = (age <= 18) ? "yes" : "no";

var a = 1 + 2 * 3; // 2 * 3 が優先される
var b = (1 + 2) * 3;  // カッコを使って優先順位を変更できる

if (a > b) {
    // a が b よりも大きいとき
} else {
    // a は b 以下
}

if (a > b) {
    // a が b よりも大きい時
} else if (a > c) {
    // a が c よりも大きい時
} else {
    // それ以外の時
}

switch (char) {
    case 'a':
        // do something if char is 'a'
        break;
    case 'b':
        // do something if char is 'b'
        break;
    case 'c':
        // do something if char is 'c'
        break;
    case 'd':
        // do something if char is 'd'
        break;
    case 'e':
    case 'f':
        // do something if char is 'e' or 'f'
        break;
        // 何にも一致しなかった時
    default:
        break;
}

switch (num) {
    case 1:
        // do something if num is 1
        break;
    case 2:
        // do something if num is 2
    case 3:
        // do something if num is 2 or 3
    case 4:
        // do something if num is 2 or 3 or 4
    default:
        // do something if num is not 1
}

var sum = 0;

for (var i = 0; i < 10; i++) {
    sum = sum + (i * 10);
}

var i = 0,
    sum = 0;

while (i < 10) {
    sum = sum + (i * 10);
    i++;
}

var i = 0,
    sum = 0;

do {
    sum = sum + (i * 10);
} while (i < 10);

var i = 0;

while (true) {  // 無限ループ
    if (i > 5) {
        break;  // i が 5 より大きくなったらループを中断
    }
}

var i = 0;

for (i = 0; i < 10; i++) {
    if (i % 2) {
        continue;   // 奇数の場合はスキップ
    }
    // 偶数の時だけここに行く
    // do something
}

var obj = {
    a: 10,
    b: 20,
    c: 30
};

var obj = {};
obj.a = 10;     // ドットシンタックス
obj.b = 20;
obj['c'] = 30;    // 連想配列風

var my = {
    namespace: {
        foo: 'baz'
    }
};

my.namespace.foo;       // 'baz'
my['namespace'].foo;  // 'baz'

var obj = {
    a: 10,
    b: 20
};

var res1 = 'a' in obj;    // true
var res2 = 'z' in obj;    // false

var obj = {};

obj.foo = 10;
obj.bar = 20;
obj.baz = 30;

for (var p in obj) {
    obj[p];
}

function funcName() {
    // do something
}

function max(a, b) {
    if (a > b) {
        return a;
    }
    return b;
}

funcName();

funcName(a, b);

var result = max(10, 20);

function pow(n) {
    if (n == 0) {
        return 1;
    }
    return pow(n - 1) * n;
}

var result = pow(5); // 120 (5!)

function funcName() {
    // do something
}

var fn = funcName;  // 変数に代入
fn();   // 呼び出し

function funcName(callback) {
    // do something...
    callback();
}

function callbackFunc() {
    // run after `funcName`
}

funcName(callbackFunc);

var fn = function() {
    // do something...
};

fn(); // 呼び出し

function doSomething(callback) {
    // do something…
    callback();
}

doSomething(function() {
    // run after `doSomething`
});

(function() {
    // run anonymous function
})();

var obj = {
    max: function(a, b) {
        if (a > b) {
            return a;
        }
        return b;
    },
    min: function(a, b) {
        if (a > b) {
            return b;
        }
        return a;
    }
};

obj.max(10, 20);    // 20
obj.min(10, 20);    // 10

function foo() {
    var a = 100;
}

var baz = a;    // baz === undefined

function foo() {
    // outer function
    function bar() {
        // inner function
        function baz() {
            // super inner function
        }
    }
}

function outer() {
    var a = 10,
        b = 20;
    function inner() {
        var c = a;  // c == 10
    }
    inner();
    var x = c;  // x === undefined
}

var a = 10, b = 20;    // どこからでも参照できてしまう

function() {
    var c = a,
        d = b;  // c == 10, d == 20
}

(function() {
    var a = 10,
        b = 20;
})();

function capsule() {
    var himitsu1 = 10,
        himitsu2 = 20;
    
    return function(a, b) {
        return a + b + himitsu1 + himitsu2;
    };
}

var fn = capsule();
var result = fn(100, 200);  // result == 330

function closure() {
    var n = 0;
    return function() {
        n++;
        return n;
    };
}

var fn = closure();

var res1 = fn(),    // 1
    res2 = fn(),    // 2
    res3 = fn();    // 3

function Person(name, age) {
    this.name = name;
    this.age = age;
    
    this.introduce = function() {
        return 'My name is ' + this.name + '. I\'m ' + age ' years old.';
    };
}

var alice = new Person('Alice Liddel', 10),
    bob = new Person('Bob Dylan', 71);

var introOfAlice = alice.introduce();   // 'My name is Alice Liddel. I'm 10 years old.'
var introOfBob = bob.introduce();   // 'My name is Bob Dylan. I'm 71 years old.'

alice.sayAboutFuture = function(n) {
    return n + ' years after, my age will be ' + (this.age + n) + '.';
};

var future = alice.sayAboutFuture(90);  // '90 years after, my age will be 100.'

try {
    // do something.
    // 例外が起きるかもしれないコード
} catch (e) {
    // 例外が起きた時に実行される
    // e にスローされたオブジェクトが渡される
} finally {
    // 例外が起きても起きなくても必ず実行される
}

try {
    if (Math.random() % 2) {
        throw new Error('なにか起きた');
    }
    // do something...
} catch (e) {
    // e.message でエラーメッセージを取得できる
}

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