JavaScript 2019 - New Features

Array.flat() function

The flat() method concatenates all sub elements of an array and returns a new array.The programmer can identify the depth of sub elements. The default depth is 1.

// Array.flat
let nestedArray = [1, [2, [3]]];
const flattened = nestedArray.flat(2);
console.log(flattened); // [1, 2, 3]
let myArr = [[1, 2], [3, 4], [5, 6]];
let newArr = myArr.flat();
console.log(newArr);// Result: [1, 2, 3, 4, 5, 6]

In the above code nestedArray object is flattened at depth 2 and myarr object is flattened at depth 1.

Array.flatMap() function

It maps each element of the host array using a callback function and returns a new array object.

let myArr = [1, 2, 3, 4, 5, 6];
let newArr = myArr.flatMap((x) => x * 2);
console.log(newArr); // Output: [2, 4, 6, 8, 10, 12]

In the above code each element of the myarr object is doubled using callback function and a new array is returned.

Catch without parameter

The catch clause parameter is optional . This simplifies exception handling.

// catch without parameter
try {
    throw 10;
}catch {
    console.log("error");
}

In the above code the catch clause does not have error object a parameter as it is optional.

String.trimStart() and String.trimEnd() functions

Both of these functions are used for removing extra spaces from start and end of the string.

// string - trimStart, trimEnd
let text = '   Namaste, JavaScript!   ';
let trimmedStart = text.trimStart();
const trimmedEnd = text.trimEnd();
console.log(trimmedStart); // Output: Namaste, JavaScript!
console.log(trimmedEnd); // Output:  Namaste, JavaScript!

In the above code the extra space from text string is remove from starting and ending of the string.

Object.fromEntries() function

It is used for converting a list of k/v pair to an object. The list should have data in the key/value format.

// fromEntries - array to object - which has KV
const entries = [['a', 1], ['b', 2]];
const obj = Object.fromEntries(entries);
console.log(obj); // Output: { a: 1, b: 2 }

In the above code the 2D array is converted to an object with key/value pairs.

// map to object - fromEntries
const map = new Map([
    ["Lang", "JS"],
    ["lang2", "JS2"],
  ]);
let obj2 = Object.fromEntries(map);
console.log(obj2); // {Lang: 'JS', lang2: 'JS2'}

In the above code map object is converted to an object.

Symbol.description

The symbol object has a new description property which provides generic information about the Symbol object

// Symbol.description
let mySymbol = Symbol('My custom symbol');
console.log(mySymbol.description); // Output: 'My custom symbol'

In the above code the Symbol object's generic information can be got using description property.

Complete Code Listing

// Array.flat
let nestedArray = [1, [2, [3]]];
const flattened = nestedArray.flat(2);
console.log(flattened); // [1, 2, 3]
let myArr = [[1, 2], [3, 4], [5, 6]];
let newArr = myArr.flat();
console.log(newArr);// Result: [1, 2, 3, 4, 5, 6]

 myArr = [1, 2, 3, 4, 5, 6];
 newArr = myArr.flatMap((x) => x * 2);
console.log(newArr); // Output: [2, 4, 6, 8, 10, 12]

// catch without parameter
try {
    throw 10;
}catch {
    console.log("error");
}
// string - trimStart, trimEnd
let text = '   Namaste, JavaScript!   ';
let trimmedStart = text.trimStart();
const trimmedEnd = text.trimEnd();
console.log(trimmedStart); // Output: Namaste, JavaScript!
console.log(trimmedEnd); // Output:  Namaste, JavaScript!

// fromEntries - array to object - which has KV
const entries = [['a', 1], ['b', 2]];
const obj = Object.fromEntries(entries);
console.log(obj); // Output: { a: 1, b: 2 }

// map to object - fromEntries
const map = new Map([
    ["Lang", "JS"],
    ["lang2", "JS2"],
  ]);
let obj2 = Object.fromEntries(map);
console.log(obj2); // {Lang: 'JS', lang2: 'JS2'}

// Symbol.description
let mySymbol = Symbol('My custom symbol');
console.log(mySymbol.description); // Output: 'My custom symbol'