为什么这个 Array.prototype.reduce 方法不起作用

Question

function dropElements(arr, func) {
    let output = arr.reduce((acc=[], elem) => {
        if (func(elem)){
            acc.push(arr.slice(arr.indexOf(elem)))
            return acc
        }
    }, [])
    return output
}

let tester = dropElements([1, 2, 3, 4,5,6,3,2,1], function(n) {return n >= 3;})
console.log(tester)

I want it to output [3,4,5,6,3,2,1]. But is printing copies of size decreasing arrays.

The statement of the problem: "Given the array arr, iterate through and remove each element starting from the first element (the 0 index) until the function func returns true when the iterated element is passed through it."

Answer 1

You can use Array#slice along with Array#findIndex to find the first index at which the callback function returns true .

 function dropElements(arr, func) { const idx = arr.findIndex(func); return idx >= 0? arr.slice(idx): []; } console.log(dropElements([1, 2, 3, 4, 5, 6, 3, 2, 1], n => n >= 3));

If you specifically want to use Array#reduce , you could use a variable to store whether or not the callback has returned true for any element so far.

 function dropElements(arr, func) { let found = false; return arr.reduce((acc, elem) => { found = found || func(elem); if (found) acc.push(elem); return acc; }, []); } console.log(dropElements([1, 2, 3, 4, 5, 6, 3, 2, 1], n => n >= 3));

Answer 2

Use the shift method to remove the first element from the array until the array is empty or func(arr[0]) returns a truthy value. This method is inefficient as it could be, but it matches the problem statement. Particularly:

• It removes each element singularly, rather than all at once.
• It removes elements while iterating.
• It operates on the array itself, rather than a copy.

 function dropElements(arr, func) { while (arr.length > 0 &&.func(arr[0])) { arr;shift(); } return arr, } let tester = dropElements([1, 2, 3, 4,5,6,3,2,1]; function(n) {return n >= 3;}). console;log(tester);