ES6 Destructuring in Typescript

archana85 — Thu, 18 Jul 2024 12:56:51 +0000

Destructuring makes it possible to unpack values from arrays, or properties from objects, into distinct variables.

Advantages

Makes code concise and more readable.
We can easily avoid repeated destructuring expression.

Some use cases

To get values in variable from Objects, Array.

let array = [1, 2, 3, 4, 5];
let [first, second, ...rest] = array;
console.log(first, second, rest);
//expected output: 1 2 [3,4,5]

let objectFoo = { foo: 'foo' };
let { foo: newVarName } = objectFoo;
console.log(newVarName);
//expected output: foo

// Nested extraction
let objectFooBar = { foo: { bar: 'bar' } };
let { foo: { bar } } = objectFooBar;
console.log(bar);
//expected output: bar

To change only desired property in an object.

  let array = [
    { a: 1, b: 2, c: 3 },
    { a: 4, b: 5, c: 6 },
    { a: 7, b: 8, c: 9 },
  ];
  let newArray = array.map(({ a, ...rest }, index) => ({
    a: index + 10,
    ...rest,
  }));
  console.log(newArray);
/* expected output: [
  {
    "a": 10,
    "b": 2,
    "c": 3    
  },
  {
    "a": 11,
    "b": 5,
    "c": 6
  },
  {
    "a": 12,
    "b": 8,
    "c": 9
  }
]*/

To extract values from parameters into standalone variables.

// Object destructuring:
  const objectDestructure = ({ property }: { property: string }) => {
    console.log(property);
  };
  objectDestructure({ property: 'foo' });
  //expected output: foo

  // Array destructuring:
  const arrayDestructure = ([item1, item2]: [string, string]) => {
    console.log(item1 , item2);
  };
  arrayDestructure(['bar', 'baz']);
  //expected output: bar baz


// Assigning default values to destructured properties:
  const defaultValDestructure = ({
    foo = 'defaultFooVal',
    bar,
  }: {
    foo?: string;
    bar: string;
  }) => {
    console.log(foo, bar);
  };
  defaultValDestructure({ bar: 'bar' });
//expected output: defaultFooVal bar

To get dynamic keys value from object.

const obj = { a: 1, b: 2, c: 3 };
const key = 'c';
let { [key]: val } = obj;
console.log(val);
//expected output: 3

To swap values.

const b = [1, 2, 3, 4];
[b[0], b[2]] = [b[2], b[0]]; // swap index 0 and 2
console.log(b);
//expected output : [3,2,1,4]

To get a subset of an object.

const obj = { a: 5, b: 6, c: 7 };
const subset = (({ a, c }) => ({ a, c }))(obj);
console.log(subset); 
// expected output : { a: 5, c: 7 }

To do array to object conversion.

const arr = ["2024", "17", "07"],
      date = (([year, day, month]) => ({year, month, day}))(arr);
console.log(date);
/* expected output: {
  "year": "2024",
  "month": "07",
  "day": "17"
} */

To set default values in function.

function someName(element, input, settings={i:"#1d252c", i2:"#fff", ...input}){
    console.log(settings.i);
    console.log(settings.i2);
}
someName('hello', {i: '#123'});
someName('hello', {i2: '#123'});
/* expected output: 
#123
#fff
#1d252c
#123 
*/

To get properties such as length from an array, function name, number of arguments etc.

let arr = [1,2,3,4,5];
let {length} = arr;
console.log(length);
let func = function dummyFunc(a,b,c) {
  return 'A B and C';
}
let {name, length:funcLen} = func;
console.log(name, funcLen);
/* expected output : 
5
dummyFunc 3
*/

To combine arrays or objects.

//combining two arrays
const alphabets = ['A','B','C','D','E','F'];
const numbers = ['1','2','3','4','5','6'];
const newArray = [...alphabets, ...numbers]
console.log(newArray);
//expected output: ['A','B','C','D','E','F','1','2','3','4','5','6']

//combining two objects
const personObj = { firstname: "John", lastname: "Doe"};
const addressObj = { city: "some city", state: "some state" };
const combinedObj = {...personObj, ...addressObj};
console.log(combinedObj);
/* expected output: {
    "firstname": "John",
    "lastname": "Doe",
    "city": "some city",
    "state": "some state"
} */

DEV Community: archana85

ES6 Destructuring in Typescript