Skip to content
Announcing the new Pro Zone. Check it out!

concat() JavaScript Array Method – How to Merge Arrays

Whenever you use concat() on an array, the method does the following:

  1. It concatenates (merges) its calling array with its arguments.
  2. It creates and populates a new array with the merged values.

Syntax of the concat() Method

concat() accepts one or more arguments. Here is the syntax:

callingArray.concat(item1, item2, ..., itemX)

The item arguments are the values you wish to concatenate into the callingArray.

Examples

Below are examples of the concat() method.

How to merge an array with another array

// Define two arrays:
const array1 = [1, 2, 3];
const array2 = [4, 5, 6];
// Merge array1 with array2:
const newArray = array1.concat(array2);
// Log the newArray to the console:
console.log(newArray);
// The invocation above will return:
// [1, 2, 3, 4, 5, 6]

Try it on StackBlitz

The snippet above used concat() to concatenate (merge) array1 with array2.

How to merge an array with three other arrays

// Define four arrays:
const array1 = [1, 2, 3];
const array2 = [4, 5, 6];
const array3 = ["a", "b"];
const array4 = ["pink", 100, true];
// Merge array1 with array2, array3, and array4:
const newArray = array1.concat(array2, array3, array4);
// Log the newArray to the console:
console.log(newArray);
// The invocation above will return:
// [1, 2, 3, 4, 5, 6, "a", "b", "pink", 100, true]

Try it on StackBlitz

The snippet above used concat() to concatenate four arrays.

How to merge an array with a nested array

// Define two arrays:
const array1 = [1, 2, 3];
const array2 = [4, ["a", "b"], 5, 6, ["pink", 100, true]];
// Merge array1 with array2:
const newArray = array1.concat(array2);
// Log the newArray to the console:
console.log(newArray);
// The invocation above will return:
// [1, 2, 3, 4, ["a", "b"], 5, 6, ["pink", 100, true]]

Try it on StackBlitz

The snippet above used concat() to merge array1 with a nested array.

CodeSweetly ads

Express Your Love for Coding!

Explore CodeSweetly's Shop for an array of stylish products to enhance your coding experience.
Shop now

How to merge two nested arrays

// Define two arrays:
const array1 = [1, ["pink", 100, true], 2, 3];
const array2 = [4, ["a", "b"], 5, 6];
// Merge array1 with array2:
const newArray = array1.concat(array2);
// Log the newArray to the console:
console.log(newArray);
// The invocation above will return:
// [1, ["pink", 100, true], 2, 3, 4, ["a", "b"], 5, 6]

Try it on StackBlitz

The snippet above used concat() to merge two nested arrays.

How to merge an array with a number

// Define an array:
const array1 = [1, 2, 3];
// Merge array1 with a number:
const newArray = array1.concat(4);
// Log the newArray to the console:
console.log(newArray);
// The invocation above will return:
// [1, 2, 3, 4]

Try it on StackBlitz

The snippet above used concat() to merge array1 with a number.

How to merge an array with three numbers

// Define an array:
const array1 = [1, 2, 3];
// Merge array1 with three numbers:
const newArray = array1.concat(4, 75, 29);
// Log the newArray to the console:
console.log(newArray);
// The invocation above will return:
// [1, 2, 3, 4, 75, 29]

Try it on StackBlitz

The snippet above used concat() to merge array1 with three numbers.

How to merge an array with two strings

// Define an array:
const array1 = [1, 2, 3];
// Merge array1 with two strings:
const newArray = array1.concat("a", "b");
// Log the newArray to the console:
console.log(newArray);
// The invocation above will return:
// [1, 2, 3, "a", "b"]

Try it on StackBlitz

The snippet above used concat() to merge array1 with two strings.

How to merge an array with a number, string, and another array

// Define two arrays:
const array1 = [1, 2, 3];
const array2 = [4, 5, 6];
// Merge array1 with a number, string, and array2:
const newArray = array1.concat(910, "CodeSweetly", array2);
// Log the newArray to the console:
console.log(newArray);
// The invocation above will return:
// [1, 2, 3, 910, "CodeSweetly", 4, 5, 6]

Try it on StackBlitz

The snippet above used concat() to concatenate array1 with three other items.

How to merge an array with an object

// Define an array:
const array1 = [1, 2, 3];
// Merge array1 with an object:
const newArray = array1.concat({ year: 2022, month: "October" });
// Log the newArray to the console:
console.log(newArray);
// The invocation above will return:
// [1, 2, 3, {year: 2022, month: "October"}]

Try it on StackBlitz

The snippet above used concat() to merge array1 with an object.