JavaScript ES2019 中的 8 个新功能

try {  // trying to use a new ES2019 feature  // which may not be implemented in other browsers} catch (unused) {  // revert back to old way}

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

const LS = eval('"\u2028"');const PS = eval("'\u2029'");

const mySymbol = Symbol('myDescription');console.log(mySymbol); // Symbol(myDescription)console.log(mySymbol.toString()); // Symbol(myDescription)console.log(mySymbol.description); // myDescription

function /* comment */ foo /* another comment */ (){}
// Beforeconsole.log(foo.toString()); // function foo(){}
// Now ES2019console.log(foo.toString()); // function /* comment */ foo /* another comment */ (){}
// Arrow Syntaxconst bar /* comment */ = /* another comment */ () => {} console.log(bar.toString()); // () => {}

const obj = {    prop1: 1,    prop2: 2,}; const entries = Object.entries(obj);console.log(entries); // [ [ 'prop1', 1 ], [ 'prop2', 2 ] ]const fromEntries = Object.fromEntries(entries);console.log(fromEntries); // Object { prop1: 1, prop2: 2 }console.log(obj === fromEntries); // false

const obj = {    prop1: 1,    prop2: 2,    deepCopy: {        mutateMe: true    }}; const entries = Object.entries(obj);const fromEntries = Object.fromEntries(entries);fromEntries.deepCopy.mutateMe = false;console.log(obj.deepCopy.mutateMe); // false

// Beforeconsole.log(JSON.stringify('\uD800')); // "�" // Now ES2019console.log(JSON.stringify('\uD800')); // "\ud800"

// Trimconst name = "   Codedam ";console.log(name.trim());   // "Codedam"
// Trim Startconst description = "   Unlocks Secret Codes ";console.log(description.trimStart());   // "Unlocks Secret Codes " // Trim Endconst category = "  JavaScript ";console.log(category.trimEnd());    // "  JavaScript"

const arr = [1, 2, [3, 4, [5, 6]]];arr.flat(); // [1, 2, 3, 4, [5, 6]]arr.flat(2); // [1, 2, 3, 4, 5, 6]
// You can use Infinity to flatten all the nested arrays no matter how deep the array is const arrExtreme = [1, [2, [3, [4, [5, 6, 7, [8, 9]]]]]];arrExtreme.flat(Infinity); // [1, 2, 3, 4, 5, 6, 7, 8, 9]

const arr = ['Codedam', 'is Awsome', '!']; const mapResult = arr.map(item => item.split(' '));console.log(mapResult); // [ [ 'Codedam' ], [ 'is', 'Awsome' ], [ '!' ] ] const flatMapResult = arr.flatMap(chunk => chunk.split(' '));console.log(flatMapResult); // ['Codedam', 'is',  'Awsome', '!'];