TypedArray.prototype.slice()

The slice() method returns a new typed array (with a new underlying buffer), that contains a copy of a portion of the original typed array. This method has the same algorithm as Array.prototype.slice(). TypedArray is one of the typed array types here.

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Syntax

slice()
slice(start)
slice(start, end)

Parameters

start 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 start 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 the original typed array, but instead returns a copy of a portion of the original typed array. As typed arrays only store primitive values, the copy the slice method returns is always a shallow copy.

If an element is changed in either typed array, the other typed array is not affected.

Examples

Return a portion of an existing typed array

const 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. 

if (!Uint8Array.prototype.slice) {
  Object.defineProperty(Uint8Array.prototype, 'slice', {
    value: function (begin, end)
     {
        return new Uint8Array(Array.prototype.slice.call(this, begin, end));
     }
  });
}

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

Specifications

Specification
ECMAScript Language Specification
# sec-%typedarray%.prototype.slice

Browser compatibility

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See also