js converts a multidimensional array into a one-dimensional array and then reorders it

// For example, here is a multidimensional array let arr = [1, 1, 2, [4, 2, [1, 3, [4, 2, 1]], 5], 2, 5, 3]
console.log(arr.flat(2)); // Specify the number of nested levels // Output [ 1, 1, 2, 4, 2, 1, 3, [ 4, 2, <1 empty item>, 1 ], 5, 2, 5, 3 ]

console.log(arr.flat(Infinity)); // No matter how many levels of nesting there are, // Output: [ 1, 1, 2, 4, 2, 1, 3, 4, 2, 1, 5, 2, 5, 3 ]

// Still this array let arr = [1, 1, 2, [4, 2, [1, 3, [4, 2, 1]], 5], 2, 5, 3]
// When characters are operated with other basic data types, they will all be converted into characters. Then call the split() method to split them with ',' console.log((arr + '').split(','));
// Output ['1', '1', '2', '4', '2', '1', '3', '4', '2', '1', '5', '2', '5', '3']

// The output is not very good, let's continue to optimize it // Still using this array let arr = [1, 1, 2, [4, 2, [1, 3, [4, 2, 1]], 5], 2, 5, 3]
let newArr = (arr + '').split(',')
let arr1 = []
newArr.forEach((items) => {
    arr1.push(+items) // '+items' convert data type})
console.log(arr1);
// Output [ 1, 1, 2, 4, 2, 1, 3, 4, 2, 1, 5, 2, 5, 3 ]

let arr = [1, 1, 2, [4, 2, [1, 3, [4, 2, 1]], 5], 2, 5, 3]
let newArr = arr.toString().split(',')
let arr1 = []
newArr.forEach((items) => {
    arr1.push(+items)
})
console.log(arr1);
// Output ['1', '1', '2', '4', '2', '1', '3', '4', '2', '1', '5', '2', '5', '3']

let arr = [1, 1, 2, [4, 2, [1, 3, [4, 2, 1]], 5], 2, 5, 3]
let newArr = arr.join().split(',')
console.log(newArr)
// Output ['1', '1', '2', '4', '2', '1', '3', '4', '2', '1', '5', '2', '5', '3']

function a() {
    if (a <= 1) {
        return 1
    } else {
        return a * fn(a - 1)
    }
}

let arr = [1, 1, 2, [4, 2, [1, 3, [4, 2, 1]], 5], 2, 5, 3]
let newArr = []

let fn = (arr) => {
    for (let i = 0; i < arr.length; i++) {
        // Determine if the traversed value is still an array and continue traversing if (Array.isArray(arr[i])) { // Use array Array.isArray() to determine whether the passed value is an Array
            fn(arr[i])
            // If the traversed value is not an array, push it into the new array newArr} else {
            newArr.push(arr[i])
        }
    }
}
fn(arr)
console.log(newArr);

const arr = [1, 1, 2, [4, 2, [1, 3, [4, 2, 1]], 5], 2, 5, 3]
const fn = (array) => {
    return array.reduce((prev, curr) => {
        // Check if curr is an array return prev.concat(Array.isArray(curr) ? fn(curr) : curr)
    }, [])
}
console.log(fn(arr))

const arr = [1, 1, 2, 4, 2, 1, 3, 4, 2, 1, 5, 2, 5, 3]
const fn = (arr) => {
    const newArr = []
    for (let i = 0; i < arr.length; i++) {
        if (newArr.indexOf(arr[i]) == -1) {
            newArr.push(arr[i])
        }
    }
    return newArr
}
console.log(fn(arr));

const arr = [1, 1, 2, 4, 2, 1, 3, 4, 2, 1, 5, 2, 5, 3]
// Using the Set data structure provided by ES6, the new Set members are unique, and then the data is expanded and stored in the array const newArr = [...new Set(arr)]
console.log(newArr);

// Alternatively, you can use the Array.from() method to convert an array-like object or a traversable object into a real array.
const newArr = Array.from(new Set(arr))
console.log(newArr);

const arr = [1, 1, 2, 4, 2, 1, 3, 4, 2, 1, 5, 2, 5, 3]
const newArr = arr.filter((value, index, array) => { // Pass three parameters, value, index, and original array, return array.indexOf(value) == index // indexOf always returns the index of the first value. The index of the subsequent duplicate values ​​is not equal to the position returned by indexOf and will be filtered out by filter})
console.log(newArr);

const arr = [1, 23, 1, 1, 1, 3, 23, 5, 6, 7, 9, 9, 8, 5, 5, 5];
const fn = (a, b) => {
    return a - b // b - a in reverse order}
console.log(arr.sort(fn));