What’s new in JavaScript ES10 (ES2019)?

ES which stands for ECMAScript is a standardized specification of a scripting language. Initially it was named as Mocha and finally as JavaScript. So far there are ten editions published.

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The new features of ES10 includes flat(), flatMap(), object.fromEntries(), trimStart(), optional catch binding and many more. In this post, we will take a look at these new features and see how they upgrade the language.

1. flat() and flatMap()

The flat() method flattens the array by a given depth. The default flat level is 1. The flat(Infinity) method flattens the array to the last depth of the array.

const Numbers = [12,3,3,[33,3,4,55,[34,6,7,9,0]]];
console.log(Numbers.flat()); // Default flat level is 1
// output : [12, 3, 3, 33, 3, 4, 55, Array(5)]
console.log(Numbers.flat(Infinity));
// output : [12, 3, 3, 33, 3, 4, 55, 34, 6, 7, 9, 0]

The flatMap() method first maps each element using a mapping function and then, flattens the result into a new array.

const Numbers = [1,2,3,4,5,6];
const alphaNumber = ['one', 'two', 'three', 'four', 'five', 'six'];
const mappedAndFlattenedExample = Numbers.flatMap((number, index) => [
  number,
  alphaNumber[index]
]);
console.log(mappedAndFlattenedExample);
// output : [1, 'one', 2, 'two', 3, 'three', 4, 'four', 5, 'five', 6, 'six']

2. trimStart() and trimEnd()

The trimStart() / trimLeft() methods removes whitespaces from the beginning of the string.

const greeting = '   Hello world!   ';
console.log(greeting);
//output: "   Hello world!   ";
console.log(greeting.trimStart());
//output: "Hello world!   ";

The trimEnd() / trimRight() methods remove whitespaces from the end of the string.

const greeting = '   Hello world!   ';
console.log(greeting);
//output: "   Hello world!   ";
console.log(greeting.trimEnd());
//output: "   Hello world!";

3. Object.fromEntries()

The Object.fromEntries() method transforms a list of key-value pairs into an object.

const entries = new Map([
  ['foo', 'bar'],
  ['baz', 42]
]);
const obj = Object.fromEntries(entries);
console.log(obj);
//output: Object { foo: "bar", baz: 42 }

4. Optional Catch Binding

One of the new features they came up with is the ability to not to bind the error parameter within the catch close.

try {
      throw "Error not bothered about";
    } catch {
      // logic..
    }

5. Description property for Symbol objects

When creating symbols, now you can add a description to it for debugging purposes. It’ll return a string containing the description of the symbol.

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

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

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