Array.prototype.slice()
The slice() method returns a shallow copy of a portion of an array into a new array object selected from begin to end ( end not included). The original array will not be modified.
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 ( arr.length ). If end is greater than the length of the sequence, slice extracts through the end of the sequence ( arr.length ).
Return value
A new array containing the extracted elements.
Description
slice does not alter the original array. It returns a shallow copy of elements from the original array. Elements of the original array are copied into the returned array as follows:
- For object references (and not the actual object), slice copies object references into the new array. Both the original and new array refer to the same object. If a referenced object changes, the changes are visible to both the new and original arrays.
- For strings, numbers and booleans (not String. Number and Boolean objects), slice copies the values into the new array. Changes to the string, number or boolean in one array do not affect the other array.
If a new element is added to either array, the other array is not affected.
Return a portion of an existing array
Using slice
In the following example, slice creates a new array, newCar. from myCar. Both include a reference to the object myHonda. When the color of myHonda is changed to purple, both arrays reflect the change.
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Array-like objects
slice method can also be called to convert Array-like objects / collections to a new Array. You just bind the method to the object. The arguments inside a function is an example of an 'array-like object'.
Binding can be done with the. call function of Function.prototype and it can also be reduced using [].slice.call(arguments) instead of Array.prototype.slice.call. Anyway, it can be simplified using bind .
Streamlining cross-browser behavior
Although host objects (such as DOM objects) are not required by spec to follow the Mozilla behavior when converted by Array.prototype.slice and IE < 9 does not do so, versions of IE starting with version 9 do allow this. “Shimming†it can allow reliable cross-browser behavior. As long as other modern browsers continue to support this ability, as currently do IE, Mozilla, Chrome, Safari, and Opera, developers reading (DOM-supporting) slice code relying on this shim will not be misled by the semantics; they can safely rely on the semantics to provide the now apparently de facto standard behavior. (The shim also fixes IE to work with the second argument of slice() being an explicit null / undefined value as earlier versions of IE also did not allow but all modern browsers, including IE >= 9, now do.)