Question

How to insert an item into an array at a specific index in JavaScript

Answer 1

var arr = ["a", "b", "c", "d", "e"];

Array.prototype.insert = function(index) {
  this.splice.apply(this, [index, 0].concat(
    Array.prototype.slice.call(arguments, 1)));
  return this;
};

arr = arr.insert(3, "W", "Z").slice(1, 5);
    
document.write(arr);
    

/*
run:

b,c,W,Z
  
*/

 

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Answer 2

var arr = ["a", "b", "c", "d", "e"];

Array.prototype.insert = function(index) {
  this.splice.apply(this, [index, 0].concat(
    Array.prototype.slice.call(arguments, 1)));
  return this;
};

arr = arr.insert(2, "W", "Z").slice(1, 4);
    
document.write(arr);
    

/*
run:

b,W,Z
  
*/

 

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Answer 3

var arr = ["a", "b", "c", "d", "e"];

Array.prototype.insert = function(index) {
  index = Math.min(index, this.length);
  arguments.length > 1
    && this.splice.apply(this, [index, 0].concat([].pop.call(arguments)))
    && this.insert.apply(this, arguments);
  return this;
};

arr = arr.insert(2, "W", "X").join("-");
    
document.write(arr);
    

/*
run:

a-b-W-X-c-d-e
  
*/

 

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Answer 4

const arr = ['a', 'b'];

arr.splice(1, 0, 'c');

document.write(arr);

 
 
/*
run:
       
a,c,b 
     
*/

 

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