const arr1 = [1, 2, [3, 4]];
arr1.flat(); 
// [1, 2, 3, 4]

const arr2 = [1, 2, [3, 4, [5, 6]]];
arr2.flat(2); 
// [1, 2, 3, 4, 5, 6]

const arr3 = [1, 2, [3, 4, [5, 6, [7, 8]]]];
arr3.flat(Infinity); 
// [1, 2, 3, 4, 5, 6, 7, 8]

const arr4 = [1, 2, , 4, 5];
arr4.flat(); // [1, 2, 4, 5]

const arr1 = [1, 2, 3];

arr1.map(x => [x * 4]); 
// [[4], [8], [12]]

arr1.flatMap(x => [x * 4]); 
// [4, 8, 12]

const sentence = ["This is a", "regular", "sentence"];

sentence.map(x => x.split(" ")); 
// [["This","is","a"],["regular"],["sentence"]]

sentence.flatMap(x => x.split(" ")); 
// ["This","is","a","regular", "sentence"]

// 可以使用 归纳（reduce） 与 合并（concat）实现相同的功能
sentence.reduce((acc, x) => acc.concat(x.split(" ")), []);

const test = " hello ";

test.trim(); // "hello";
test.trimStart(); // "hello ";
test.trimEnd(); // " hello";

const obj = { prop1: 2, prop2: 10, prop3: 15 };

// 转化为键值对数组：
let array = Object.entries(obj); 
// [["prop1", 2], ["prop2", 10], ["prop3", 15]]

array = array.map(([key, value]) => [key, Math.pow(value, 2)]); 
// [["prop1", 4], ["prop2", 100], ["prop3", 225]]

const newObj = Object.fromEntries(array); 
// {prop1: 4, prop2: 100, prop3: 225}

try {
 //...
} catch (er) {
 //handle error with parameter er
}

try {
 //...
} catch {
 //handle error without parameter
}

const testSymbol = Symbol("Desc");

testSymbol.description; // "Desc"

testSymbol.toString(); // "Symbol(Desc)"

function /* foo comment */ foo() {}

foo.toString(); // "function foo() {}"

foo.toString(); // "function /* foo comment */ foo() {}"

var str = '{"name":"Bottle\u2028AnGe"}'
JSON.parse(str)
// {name: "Bottle"}