Paige's Journey🎈

Spread syntax

• if you want to add array inside middle of array

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  const spread = [1, 2, 3]; const arr = [0, ...spread, 4]; // [0, 1, 2, 3, 4])

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• if it is empty array, it will return nothing

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  const spread = []; const arr = [0, ...spread, 4]; // [0, 4]

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• can merge arrays same as concat method

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  const arr1 =[1, 2, 3]; const arr2 = [3, 4, 5]; const concatenated = [...arr1, ...arr2]; // [0, 1, 2, 3, 4, 5] arr1.concat(arr2); // [0, 1, 2, 3, 4, 5]

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• can merge objects as well

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  const paige = {     firstName: 'Paige',     LastName: 'Kim', }; const me = {     hobby: 'piltaes',     todos: ['coplit', 'koans'], };   const merged = {...paige, ...me}; /* const merged = {     firstName: 'Paige',     LastName: 'Kim',     hobby: 'piltaes',     todos: ['coplit', 'koans'], }; */ Colored by Color Scripter

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• if spread syntax goes inside parameter, it become 'rest parameter(rest syntax)'
  • useful when numbers of parameters were not set
  • returns arguments with 'ARRAY'

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    function pintMaxNums(...args) {      console.log(args); //[10, 30, 40] } pintMaxNums(10, 30, 40);

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Object

• === 
  • To compare 'REFERENCE' only in object!!
    

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    const person = {       son: {         age: 9,       },     };      const boy = person.son; boy.age = 20; expect(person.son.age).toBe(20); expect(person.son === boy).toBe(true); expect(person.son === { age: 9 }).toBe(false); expect(person.son === { age: 20 }).toBe(false);

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