浅谈目前可以使用ES10的5个新特性

const obj = {one: 1, two: 2, three: 3};

console.log(Object.entries(obj));  
// => [["one", 1], ["two", 2], ["three", 3]]

const myArray = [['one', 1], ['two', 2], ['three', 3]];
const obj = Object.fromEntries(myArray);

console.log(obj);  // => {one: 1, two: 2, three: 3}

const myArray = [['one', 1], ['two', 2], ['three', 3]];
const Array.from(myArray).reduce((acc, [key, val]) 
=> Object.assign(acc, {[key]: val}), {})

console.log(obj);  // => {one: 1, two: 2, three: 3}

const map = new Map();
map.set('one', 1);
map.set('two', 2);

const obj = Object.fromEntries(map);

console.log(obj);  // => {one: 1, two: 2}

const obj = {a: 4, b: 9, c: 16};

// 将对象转换为数组
const arr = Object.entries(obj);

// 计算数字的平方根
const map = arr.map(([key, val]) => [key, Math.sqrt(val)]);

// 将数组转换回对象
const obj2 = Object.fromEntries(map);

console.log(obj2); // => {a: 2, b: 3, c: 4}

const paramsString = 'param1=foo&param2=baz';
const searchParams = new URLSearchParams(paramsString);

Object.fromEntries(searchParams);  // => {param1: "foo", param2: "baz"}

const str = "  string  ";

// es2019
console.log(str.trimStart());  // => "string  "
console.log(str.trimEnd());   // => "  string"

// 相同结果
console.log(str.trimLeft());   // => "string  "
console.log(str.trimRight());  // => "  string"

const arr = ['a', 'b', ['c', 'd']];
const flattened = arr.flat();

console.log(flattened);  // => ["a", "b", "c", "d"]

const arr = ['a', 'b', ['c', 'd']];
const flattend = [].concat.apply([], arr);

// or
// const flattened = [].concat(...arr);

console.log(flattened);  // => ["a", "b", "c", "d"]

const arr = ['a', , , 'b', ['c', 'd']];
const flattened = arr.flat();

console.log(flattened);  // => ["a", "b", "c", "d"]

const arr = [10, [20, [30]]];

console.log(arr.flat());   // => [10, 20, [30]]
console.log(arr.flat(1));  // => [10, 20, [30]]
console.log(arr.flat(2));  // => [10, 20, 30]

const arr = [4.25, 19.99, 25.5];

console.log(arr.map(value => [Math.round(value)]));  
// => [[4], [20], [26]]

console.log(arr.flatMap(value => [Math.round(value)]));  
// => [4, 20, 26]

const arr = [[7.1], [8.1], [9.1], [10.1], [11.1]];

// do not include items bigger than 9
arr.flatMap(value => {
 if (value >= 10) {
  return [];
 } else {
  return Math.round(value);
 }
}); 

// returns:
// => [7, 8, 9]

let sym = Symbol('foo');
console.log(sym.description);  // => foo

sym = Symbol();
console.log(sym.description);  // => undefined

// create a global symbol
sym = Symbol.for('bar');
console.log(sym.description);  // => bar

try {
 // 使用浏览器可能尚未实现的功能
} catch (unused) {
 // 这里回调函数中已经帮我们处理好的错误
}

try {
 // ...
} catch {
 // ....
}

const re = /(Dr\. )\w+/g;
const str = 'Dr. Smith and Dr. Anderson';
const matches = str.matchAll(re);

for (const match of matches) {
 console.log(match);
}

// logs:
// => ["Dr. Smith", "Dr. ", index: 0, input: "Dr. Smith and Dr. Anderson", groups: undefined]
// => ["Dr. Anderson", "Dr. ", index: 14, input: "Dr. Smith and Dr. Anderson", groups: undefined]

const re = /(Dr\.) \w+/g;
const str = 'Dr. Smith and Dr. Anderson';
let matches;

while ((matches = re.exec(str)) !== null) {
 console.log(matches);
}

// logs:
// => ["Dr. Smith", "Dr.", index: 0, input: "Dr. Smith and Dr. Anderson", groups: undefined]
// => ["Dr. Anderson", "Dr.", index: 14, input: "Dr. Smith and Dr. Anderson", groups: undefined]

const re = /page (\d+)/g;
const str = 'page 2 and page 10';

console.log(str.match(re));  
// => ["page 2", "page 10"]

console.log(...str.matchAll(re)); 
// => ["page 2", "2", index: 0, input: "page 2 and page 10", groups: undefined] 
// => ["page 10", "10", index: 11, input: "page 2 and page 10", groups: undefined]