Detailed explanation of the usage of Array.copyWithin() function in ES6

ES6 adds the copyWithin function to Array, which is used to operate the current array itself and copy and overwrite elements at certain positions to other positions. The following focuses on introducing the usage of the Array.copyWithin() function in ES6. Friends who need it can refer to

ES6 adds the copyWithin function to Array, which is used to operate the current array itself and to copy certain positions. The element is copied and overlaid elsewhere.

Array.prototype.copyWithin(target, start = 0, end = this.length)

This function has three parameters.

target: destination starting position.

start: The starting position of the copy source, which can be omitted or a negative number.

end: The end position of the copy source, which can be omitted or a negative number. The actual end position is end-1.

Example:

Copy and overwrite the 3rd element (starting from 0) to the 5th element to the position starting from the 1st position.

The red block below is the starting position of the copy target, and the yellow block is the copy source.

const arr1 = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]
arr1.copyWithin(1, 3, 6)
console.log('%s', JSON.stringify(arr1))

Result:

[1,4,5,6,5,6,7,8,9,10,11]

Both start and end can be omitted.

The omission of start means starting from 0, and the omission of end means the length value of the array.

If the target position is not enough, cover as much as you can.

const arr2 = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]
arr2.copyWithin(3)
console.log('%s', JSON.stringify(arr2))

Result:

[1,2,3,1,2,3,4,5,6,7,8]

Both start and end can be negative numbers, and the negative number indicates the number counted from the right.

const arr3 = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]
arr3.copyWithin(3, -3, -2)
console.log('%s', JSON.stringify(arr3))

Result:

[1,2,3,9,5,6,7,8,9,10,11]

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