JS ショートコード・ショートハンド集

const x = 20;
let answer;
if (x > 10) {
    answer = 'is greater';
} else {
    answer = 'is lesser';
}

if (variable1 !== null || variable1 !== undefined || variable1 !== '') {
     let variable2 = variable1;
}

let x;
let y;
let z = 5;

if (likeJavaScript === true)

let a;
if ( a !== true ) {
// do something...
}

for (let i = 0; i < allImgs.length; i++)

let dbHost;
if (process.env.DB_HOST) {
  dbHost = process.env.DB_HOST;
} else {
  dbHost = 'localhost';
}

for (let i = 0; i < 10000; i++) {}

const obj = { x:x, y:y };

function sayHello(name) {
  console.log('Hello', name);
}

setTimeout(function() {
  console.log('Loaded')
}, 2000);

list.forEach(function(item) {
  console.log(item);
});

var fn = function (a, b) {
  return a + b;
};

function calcCircumference(diameter) {
  return Math.PI * diameter
}

function volume(l, w, h) {
  if (w === undefined)
    w = 3;
  if (h === undefined)
    h = 4;
  return l * w * h;
}

const welcome = 'You have logged in as ' + first + ' ' + last + '.'

const db = 'http://' + host + ':' + port + '/' + database;

const observable = require('mobx/observable');
const action = require('mobx/action');
const runInAction = require('mobx/runInAction');

const store = this.props.store;
const form = this.props.form;
const loading = this.props.loading;
const errors = this.props.errors;
const entity = this.props.entity;

const lorem = 'Lorem ipsum dolor sit amet, consectetur\n\t'
    + 'adipisicing elit, sed do eiusmod tempor incididunt\n\t'
    + 'ut labore et dolore magna aliqua. Ut enim ad minim\n\t'
    + 'veniam, quis nostrud exercitation ullamco laboris\n\t'
    + 'nisi ut aliquip ex ea commodo consequat. Duis aute\n\t'
    + 'irure dolor in reprehenderit in voluptate velit esse.\n\t'

// joining arrays
const odd = [1, 3, 5];
const nums = [2 ,4 , 6].concat(odd);

// cloning arrays
const arr = [1, 2, 3, 4];
const arr2 = arr.slice();

function foo(bar) {
  if(bar === undefined) {
    throw new Error('Missing parameter!');
  }
  return bar;
}

const pets = [
  { type: 'Dog', name: 'Max'},
  { type: 'Cat', name: 'Karl'},
  { type: 'Dog', name: 'Tommy'},
]

function findDog(name) {
  for(let i = 0; i<pets.length; ++i) {
    if(pets[i].type === 'Dog' && pets[i].name === name) {
      return pets[i];
    }
  }
}

function validate(values) {
  if(!values.first)
    return false;
  if(!values.last)
    return false;
  return true;
}

console.log(validate({first:'Bruce',last:'Wayne'})); // true

Math.floor(4.9) === 4  //true

1+0.5;

Math.floor(1.2345)

a=Math.round(10.3);
b=Math.round(10.6);
console.log(a,b);
// 10 11

Math.pow(-3,2)

z='abcdefg';
if(z.indexOf('a')!==-1){
  console.log('a in z');
} else {
  console.log('a not in z');
}
// 'a in z'

true,false

'あいうえお'.charAt(2)
// う

a='abcdefg'.split('');

aaaaaaaaaaaaaa

Math.random()*2&1
// 0か1の乱数を生成する

a=[1,2,3],b=[4,5,6];
a.push.apply(a,b);
console.log(a);

a={z1:1,z2:2,z3:3}
b={z2:4,z3:5,z4:6}
c=Object.assign(a,b) // 18文字
console.log(c)

a=[1,2,3,4,5,6];
b=a.slice(1);
console.log(b);

a='10';
console.log(parseInt(a,16));

a=[1,2,3];
console.log(a.length>3); // 10文字

a='xyz';
console.log(a.length>3); // 10文字

console.log(window);

document.getElementById('id').innerText

new Date()
new Array()

Math.ceil(12.5),Math.ceil(0.2)

Math.ceil(1.5)+Math.floor(1.5)+Math.round(1.5);

test1.classList.add('a');
test2.classList.remove('b');
test3.classList.add('c');

setTimeout(function(){
    console.log('あ');
},1000);

setTimeout("console.log('あ')");

alert('あ'); // アラートボックスを表示する
test.classList.add('a'); // test要素にクラス名「ａ」を追加する

a='あ';
if(a=='あ'){
    console.log(a+a);
}

a=0;
if(!a){
    console.log(a);
}

var a=1,b=2,c;
if(a==1){
    c=a+b;
} else {
    c=a-b;
}
console.log(c);

typeof a==='string' // string型
typeof a==='number' // number型
typeof a==='boolean' // boolean型
typeof a.b==='undefined' // undefined
isFinite(a) // Infinity
typeof b==='function' // function型
Array.isArray(a) // Arrayオブジェクト

a=b=0;
for(var i=0;i<10;i++){
    a+=i;
    b+=i;
}
console.log(a,b);

a=b=0;
for(var i=0;i<10;i++){
    a+=i;
    b+=i;
}
console.log(a,b);

for(i=10;i--;)for(j=5;j--;)console.log(i,j);

$(document).on('keypress', function(e){
    switch (e.keyCode){
        case 39:
            console.log('next');
            break;
        case 37:
            console.log('prev');
            break;
        default:
            break;
    }
});

mes='あ';
console.log(mes);

a=1,b=2;
c=a+b;
console.log(c);

var a = new Array(),
    b = new Object;

var a = function(r){
    return 'あ'+r;
};
console.log(a('い'));

a='い',b='う';
console.log('あ'+a+b+'え\nお');