如何在特定索引处将项目插入数组中？

let ifExist = (item, strings = [ '' ], position = 0) => {
     // Output into an array with an empty string. Important just in case their isn't any item.
    let output = [ '' ];
    // Check to see if the item that will be positioned exist.
    if (item) {
        // Output should be equal to an array of strings.
        output = strings;
       // Use splice() in order to break the array.
       // Use positional parameters to state where to put the item
       // and 0 is to not replace an index. Item is the actual item we are placing at the prescribed position.
        output.splice(position, 0, item);
    }
    // Empty string is so we do not concatenate with comma or anything else.
    return output.join("");
};

然后我在下面调用它。

ifExist("friends", [ ' ( ', ' )' ], 1)}  // Output: ( friends )
ifExist("friends", [ ' - '], 1)}  // Output:  - friends
ifExist("friends", [ ':'], 0)}  // Output:   friends:

我喜欢一点安全性，所以我使用了这个：

Array.prototype.Insert = function (item, before) {
  if (!item) return;
  if (before == null || before < 0 || before > this.length - 1) {
    this.push(item);
    return;
  }
  this.splice(before, 0, item);
}


var t = ["a", "b"]

t.Insert("v", 1)

console.log(t)

//                0    1    2
const letters = ["A", "B", "D"];
const insertIndex = 2; // position in the array to insert 
const correctLetters = letters.toSpliced(insertIndex, 0, "C"); // 0 means don't delete any items, just insert. "C" is the item you want to insert.
console.log(correctLetters); // ["A", "B", "C", "D"] (new array contains new char)
console.log(letters); // ["A", "B", "D"] (unmodified)

.toSpliced(insertIndex, 0, "C", "D", "E");

以下是一段支持同时插入多个值的简单函数：

function add_items_to_array_at_position(array, index, new_items)
{
    return [...array.slice(0, index), ...new_items, ...array.slice(index)];
}

使用示例：

let old_array = [1,2,5];

let new_array = add_items_to_array_at_position(old_array, 2, [3,4]);

console.log(new_array);

//Output: [1,2,3,4,5]

var array= [10,20,30,40]

var i;

var pos=2; //pos=index + 1
/*pos is position which we want to insert at which is index + 1.position two in an array is index 1.*/

var value=5 
//value to insert

//Initialize from last array element

for(i=array.length-1;i>=pos-1;i--){

array[i+1]=array[i]

}

array[pos-1]=value

console.log(array)

我是这样做的：

const insert = (what, where, index) => 
  ([...where.slice(0, index), what , ...where.slice(index, where.length)]);

const insert = (what, where, index) =>
  ([...where.slice(0, index), what , ...where.slice(index, where.length)]);
  
const list = [1, 2, 3, 4, 5, 6];
const newList = insert('a', list, 2);

console.log(newList.indexOf('a') === 2);

export const insertItemInList = <T>(
  arr: T[],
  index: number,
  newItem: T
): T[] => [...arr.slice(0, index), newItem, ...arr.slice(index)]

多用途的数组和对象数组的可重复使用方法

let arr = [0,1,2];
let obj = [{ name: "abc"},{ name: "xyz"},{ name: "ijk"} ];

const addArrayItemAtIndex = ( array, index, newItem ) => {
    return [...array.slice(0, index), newItem, ...array.slice(index)];
}

// For Array
console.log( addArrayItemAtIndex(arr, 2,  159 ) );

// For Array of Objects
console.log( addArrayItemAtIndex(obj, 0, { name: "AMOOS"} ) );

//Suppose we have an array  
let myArray = [2, 4, 6, 8, 10];  

// Index where we want to insert the item  
let indexToInsert = 3;  

// Item we want to insert  
let itemToInsert = 174;  

// Now we Using splice() method to insert the item at the specified index  
myArray.splice(indexToInsert, 0, itemToInsert);  

// output with new value    
console.log(myArray);