# ES2019 "ES10" ^{[credit](https://blog.logrocket.com/5-es2019-features-you-can-use-today)} See the [ES2019 standard](http://www.ecma-international.org/ecma-262/10.0/) for full specification of the ECMAScript 2019 language. ES2019 includes the following new feature proposals: - [Array.prototype.{flat,flatMap}](#arrayprototypeflatflatmap) - [Object.fromEntries](#objectfromentries) - [String.prototype.{trimStart,trimEnd}](#stringprototypetrimstarttrimend) - [Symbol.prototype.description](#symbolprototypedescription) - [Optional catch binding](#optional-catch-binding) - Array.prototype.sort() is now required to be stable --- # Array.prototype.{flat,flatMap} > The flat() method enables you to easily concatenate all sub-array elements of an array. Consider the following example: ```js let arr = ['a', 'b', ['c', 'd']]; let flattened = arr.flat(); console.log(flattened); // => ["a", "b", "c", "d"] arr = ['a', , , 'b', ['c', 'd']]; flattened = arr.flat(); console.log(flattened); // => ["a", "b", "c", "d"] 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] ``` > The flatMap() method combines map() and flat() into one method. It first creates a new array with the return value of a provided function and then concatenates all sub-array elements of the array. An example should make this clearer: ```js 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] ``` # Object.fromEntries > This static method allows you to easily transform a list of key-value pairs into an object: ```js const myArray = [['one', 1], ['two', 2], ['three', 3]]; const obj = Object.fromEntries(myArray); console.log(obj); // => {one: 1, two: 2, three: 3} ``` # String.prototype.{trimStart,trimEnd} > The trimStart() and trimEnd() methods are technically the same as trimLeft() and trimRight(). These methods are currently stage 4 proposals and will be added to the specification for consistency with padStart() and padEnd(). Let’s look at some examples: ```js const str = " string "; // es2019 console.log(str.trimStart()); // => "string " console.log(str.trimEnd()); // => " string" // the same as console.log(str.trimLeft()); // => "string " console.log(str.trimRight()); // => " string" ``` > For web compatibility, trimLeft() and trimRight() will remain as aliases for trimStart() and trimEnd(). # Symbol.prototype.description > When creating a Symbol, you can add a description to it for debugging purposes. Sometimes, it’s useful to be able to directly access the description in your code. > This ES2019 proposal adds a read-only description property to the Symbol object, which returns a string containing the description of the Symbol. Here are some examples: ```js 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 ``` # Optional catch binding > This makes a small change to the ECMAScript specification that allows you to omit the catch binding and its surrounding parentheses: ```js try { // use a feature that the browser might not have implemented } catch { // do something that doesn’t care about the value thrown } ```