Je ne comprends pas pourquoi IndexOf a renvoyé -1

Question

J'ai un tableau de nombres contenant de 1 à 20. Lorsque j'utilise la méthode indexOf pour essayer de trouver la position de "2", elle apparaît à la 3ème position (correcte).

J'ai un ami nommé day = 2的变量。当我使用array.indexOf(day)的代码时，它返回-1.

Pourquoi cela arrive-t-il ?

P粉517090748 · Answer

function indexofnotworking() {
  let arr = [...new Array(20).keys()];//creat arr of numbers from 0  -19
  let arr1 = arr.slice().reverse();//make a copy and reverse it
  [...Array.from(new Array(5).keys(), x => x + 5)].forEach(n => {
    console.log('arr: %s n: %s index: %s', JSON.stringify(arr), n, arr.indexOf(n));//find the indexof n in both arrays
    console.log('arr1: %s n: %s index: %s', JSON.stringify(arr1), n, arr1.indexOf(n));/display results
  })
}

11:40:22 AM Info    arr: [0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19] n: 5 index: 5
11:40:22 AM Info    arr1: [19,18,17,16,15,14,13,12,11,10,9,8,7,6,5,4,3,2,1,0] n: 5 index: 14
11:40:22 AM Info    arr: [0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19] n: 6 index: 6
11:40:22 AM Info    arr1: [19,18,17,16,15,14,13,12,11,10,9,8,7,6,5,4,3,2,1,0] n: 6 index: 13
11:40:22 AM Info    arr: [0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19] n: 7 index: 7
11:40:22 AM Info    arr1: [19,18,17,16,15,14,13,12,11,10,9,8,7,6,5,4,3,2,1,0] n: 7 index: 12
11:40:22 AM Info    arr: [0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19] n: 8 index: 8
11:40:22 AM Info    arr1: [19,18,17,16,15,14,13,12,11,10,9,8,7,6,5,4,3,2,1,0] n: 8 index: 11
11:40:22 AM Info    arr: [0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19] n: 9 index: 9
11:40:22 AM Info    arr1: [19,18,17,16,15,14,13,12,11,10,9,8,7,6,5,4,3,2,1,0] n: 9 index: 10