0xkoji1 if..else
const x = 100
if(x>100) {
console.log('over 100!');
} else {
console.log('OK');
}
console.log((x>100) ? 'over 100!' : 'OK');
// output
OK
let result = 0;
if(result ===0) {
result = 10;
} else {
result = 100;
}
let result =0;
result = result === 0 ? 10 : 100;
// output
result 10
2 if with multiple conditions
const x = 'hello'
if(x ==='123' || x === 'world' || x === 'ok' || x === 'hello' ) {
console.log('hi 👋');
}
const myConditions = ['123', 'world', 'ok', 'hello']
if(myConditions.includes(x)) {
console.log('hi 👋');
}
// output
hi 👋
3 Variable
let a = 10;
let b = 10;
let a, b = 10;
// this won't work NG
let a = 10;
let b = 100;
let a, b = 10, 100;
// this is ok
let a = 10, b =100;
let [a, b] = [10, 100];
4 increment/decrement + α
a = a + 1;
b = b - 1;
c = c * 10;
d = d / 10;
a++;
b--;
c *= 10;
d /= 10;
5 Spread operator
const x = [1,3,5];
const y = [2,4,6];
const result = y.concat(x);
const result_with_spread = [...y, ...x];
// output
[2, 4, 6, 1, 3, 5]
6 Template literals
This isn't really short but intuitive.
Especially, if we need to put space in the text, Template literals is very useful.
x = 'hello'
console.log(x + ' world');
console.log(`${x} world`);
// output
hello world
Template literals with a new line
console.log("hello \n" + "world");
console.log(`hello
world`);
7 pow
const result = Math.pow(10, 3);
const result = 10**3
// output
1000
8 Object property
The property name and variable name must be the same.
name='koji'
sex='male'
const myObj = {name: name, sex: sex}
const anotherMyObj = {name, sex}
// output
console.log(myObj)
{name: "koji", sex: "male"}
console.log(anotherMyObj)
{name: "koji", sex: "male"}
const kojiObj = {name: "koji", sex: "male"};
const {name, sex} = kojiObj;
// output
console.log(name, sex);
koji,male
9 Repeat
const repeatNum = 10;
let resultString = '';
for(let i = 0; i < repeatNum; i ++) {
resultString += 'hi ';
}
console.log(resultString);
'hi '.repeat(repeatNum);
// output
hi hi hi hi hi hi hi hi hi hi "
cover iamge
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