Hemanth.HM

A Computer Polyglot, CLI + WEB ♥'r.

ES2019 Features

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So, it is time for an other post, this time it's ES2019 features.

Without wasting time with some placeholder content, the below are the features and examples:

Array#{flat,flatMap}

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[1, 2, 3].flatMap((x) => [x, x * 2]);
// => [1, 2, 2, 4, 3, 6]

[1, [2, [3]]].flat(Infinity);
// => [1, 2, 3]

Object.fromEntries

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const iterableOfEntries = new Map([
    ['cat', 'dog'],
    ['life', 42]
]);
const obj = Object.fromEntries(iterableOfEntries);
console.log(obj); // { cat: "dog", life: 42 }

String#{trimStart,trimEnd}

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"    Hey JS!".trimStart(); // "Hey JS!"
    "Hey JS!    ".trimEnd(); // "Hey JS!"

Symbol#description

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const symbol = Symbol('TC39');
console.log(symbol.description); // 'TC39'
console.log(symbol.hasOwnProperty('description')); // false

try { } catch {} // optional binding

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try {
    throw new Error("End of life!");
} catch { // ✋
    console.log("^ no params for catch, you are dead anyway!");
}

JSON ⊂ ECMAScript

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// extend ECMA-262 syntax into a superset of JSON.
const LS = "";
const PS = eval("'\u2029'");

well-formed JSON.stringify

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JSON.stringify('\uD800');
// → '"\\ud800"'

Function#toString

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function /* this is bar */ bar () {}

bar.toString(); // 'function /* this is bar */ foo () {}'

// ^ perviously this was not the case.

Array#sort stability

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[
  { name: "Jan",     age: 20 },
  { name: "Jhon",    age: 20 },
  { name: "David",   age: 18 },
  { name: "Ram",     age: 18 },
  { name: "Sita",    age: 18 },
  { name: "Ravan",   age: 18 },
  { name: "Asura",   age: 12 },
  { name: "Milly",   age: 12 },
].sort((m, n) => m.age - n.age));

// People with the same age retain their order.

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