JavaScript Symbol isConcatSpreadable Property

JavaScript Symbol.isConcatSpreadable is a well-known symbol used to configure if a given object should be flattened to its array elements while using the Array.prototype.concat() method.

Syntax:

Array[Symbol.isConcatSpreadable]

Here Array is the array object which is to be flattened to its array elements.

Parameters: This symbol does not accept any parameter.

Return value: This symbol does not return any value.

Example 1: In this example, we will use isConcatSpreadable Property

javascript

// Creating some arrays
const Array1 = [1, 2, 3];
const Array2 = [4, 5, 6];

// Calling concat() function
let Array3 = Array1.concat(Array2);

// Printing the concatenated array
console.log(Array3);

// Calling Symbol.isConcatSpreadable symbol
Array2[Symbol.isConcatSpreadable] = false;
Array3 = Array1.concat(Array2);

// Printing the concatenated array
// after calling of Symbol.isConcatSpreadable symbol
console.log(Array3);

Output

[ 1, 2, 3, 4, 5, 6 ]
[ 1, 2, 3, [ 4, 5, 6, [Symbol(Symbol.isConcatSpreadable)]: false ] ]

Example 2: In this example, we will use isConcatSpreadable Property

javascript

// Creating some arrays
const Array1 = [1, 2, 3];
const Array2 = [4, 5, 6];

// Calling concat() function
let Array3 = Array1.concat(Array2);

// Printing the concatenated array
console.log(Array3);

// Calling Symbol.isConcatSpreadable symbol
Array2[Symbol.isConcatSpreadable] = true;
Array3 = Array1.concat(Array2);

// Printing the concatenated array
// after calling of Symbol.isConcatSpreadable symbol
console.log(Array3);

Output

[ 1, 2, 3, 4, 5, 6 ]
[ 1, 2, 3, 4, 5, 6 ]

Supported Browsers:

• Google Chrome 48 and above
• Firefox 48 and above
• Edge 15 and above
• Opera 35 and above
• Apple Safari 10 and above