typeof undefined // "undefined"
typeof 1 // "number"
typeof true // "boolean"
typeof "str" // "string"
typeof {} // "object"
typeof [] // "object"
typeof null // "object"
typeof function(){} // "function"var a = 1;
let b = 'str';
const c = [1, 2, 3];false == false; // true
null == false; // true
undefined == false; // true
NaN == false; // true
'' == false; // true
0 == false; // true
false === false; // false
null === false; // falsefunction add(a, b) {
return a + b;
}
let addTwo = (a) => a + 2;
add(1, 2); // 3
addTwo(1); // 3class User {
constructor(firstName) {
this.firstName = firstName;
}
get fullName() {
return `${this.firstName} ${this.lastName}`;
}
set fullName(newValue) {
[this.firstName, this.lastName] = newValue.split(' ');
}
["test".toUpperCase()]() {
alert("PASSED!");
}
};new Object(); // => {}
{}; // => {}
let obj = {a: 'b'};
obj.a; // => 'b'
obj['a']; // => 'b'let obj = {a: 'b', b: 'a'};
for (key in obj) {
console.log(key, obj[key]);
// => 'a', 'b'
// => 'b', 'a'
}[1, 2, "string", {key: 'value'}] // => [1, 2, "string", {key: 'value'}]
new Array(1, 2, "string", {key: 'value'}), // => [1, 2, "string", {key: 'value'}]
new Array(4), // => [undefined, undefined, undefined, undefined]'1, 2, 3, 4'.split(', '); // => ['1', '2', '3', '4']
['1', '2', '3', '4'].join(' '); // => '1 2 3 4'
let arr = [1, 2, 3, 4];
arr.splice(1, 2); // => [2, 3]
arr; // => [1, 4];
[1, 2, 3, 4].slice(0, 2); // => [1, 2]
[1, 2, 3, 4].reverse(); // => [4, 3, 2, 1]let a = 100;
if (a >= 10) {
console.log('a >= 10');
} else {
console.log('a < 10');
}
console.log( a >= 10 ? 'a >= 10' : 'a < 10' )for (let i = 0; i < 10; i++) {
console.log(i);
}
let i = 0;
while(i < 10) {
console.log(i++);
}
let j = 0;
do {
console.log(j++);
} while (j < 10);