typedArray.slice

The slice() method returns a shallow copy of a portion of a typed array into a new typed array object. This method has the same algorithm as Array.prototype.slice(). TypedArray is one of the typed array types here.

Syntax

typedarray.slice([begin[, end]])

Parameters

begin Optional

Zero-based index at which to begin extraction.

A negative index can be used, indicating an offset from the end of the sequence. slice(-2) extracts the last two elements in the sequence.

If begin is undefined, slice begins from index 0.

end Optional

Zero-based index before which to end extraction. slice extracts up to but not including end.

For example, slice(1,4) extracts the second element through the fourth element (elements indexed 1, 2, and 3).

A negative index can be used, indicating an offset from the end of the sequence. slice(2,-1) extracts the third element through the second-to-last element in the sequence.

If end is omitted, slice extracts through the end of the sequence (typedarray.length).

Return value

A new typed array containing the extracted elements.

Description

The slice method does not alter. It returns a shallow copy of elements from the original typed array.

If a new element is added to either typed array, the other typed array is not affected.

Examples

Return a portion of an existing typed array

var uint8 = new Uint8Array([1,2,3]);
uint8.slice(1);   // Uint8Array [ 2, 3 ]
uint8.slice(2);   // Uint8Array [ 3 ]
uint8.slice(-2);  // Uint8Array [ 2, 3 ]
uint8.slice(0,1); // Uint8Array [ 1 ]

Polyfill

Since there is no global object with the name TypedArray, polyfilling must be done on an "as needed" basis.

// https://tc39.github.io/ecma262/#sec-%typedarray%.prototype.slice
if (!Uint8Array.prototype.slice) {
  Object.defineProperty(Uint8Array.prototype, 'slice', {
    value: Array.prototype.slice
  });
}

This is not a complete polyfill, since it returns an instance of Array, and not Uint8Array, so it lacks properties that would normally exist on TypedArrays.

If you need to support truly obsolete JavaScript engines that don't support Object.defineProperty, it's best not to polyfill Array.prototype methods at all, as you can't make them non-enumerable.

Specifications

Browser compatibility

See also

• Array.prototype.slice()