unshift
Add one or more elements to the beginning of a collection.
Usage
var unshift = require( '@stdlib/utils/unshift' );
unshift( collection, ...items )
Adds one or more elements to the beginning of a collection. A collection may be either an Array, Typed Array, or an array-like Object (i.e., an Object having a valid writable length property).
var arr = [ 1.0, 2.0, 3.0, 4.0, 5.0 ];
var out = unshift( arr, 6.0, 7.0 );
// returns [ 6.0, 7.0, 1.0, 2.0, 3.0, 4.0, 5.0 ]
var bool = ( out === arr );
// returns true
In contrast to Array.prototype.unshift, the function returns the extended collection, rather than the collection length. For typed arrays, the returned value is a new typed array view whose underlying ArrayBuffer may not equal the underlying ArrayBuffer for the input collection.
var ArrayBuffer = require( '@stdlib/array/buffer' );
var Float64Array = require( '@stdlib/array/float64' );
var buf = new ArrayBuffer( 3*8 ); // 8 bytes per double
var arr = new Float64Array( buf, 8, 2 );
arr[ 0 ] = 1.0;
arr[ 1 ] = 2.0;
var out = unshift( arr, 3.0 );
// returns <Float64Array>[ 3.0, 1.0, 2.0 ]
var bool = ( out === arr );
// returns false
bool = ( out.buffer === arr.buffer );
// returns true
out = unshift( out, 4.0 );
// returns <Float64Array>[ 4.0, 3.0, 1.0, 2.0 ]
bool = ( out.buffer === arr.buffer );
// returns false
Notes
- The function adds one or more elements to a typed array by setting values in the underlying
ArrayBuffer. If anArrayBufferdoes not have enough bytes in which to store all elements, the function allocates a newArrayBuffercapable of holding2^nelements, wherenis the next power of2. This procedure is similar to how environments internally handle dynamic memory allocation forArrays. - Beware when providing typed arrays which are views pointing to a shared (or pooled)
ArrayBuffer. Because the function setsArrayBufferbytes outside of a provided view, the function may overwrite bytes belonging to one or more external views. This could be a potential security vulnerability. Prefer providing typed arrays which have an exclusiveArrayBuffer; otherwise, be sure to plan for and guard against mutated state.
Examples
var Float64Array = require( '@stdlib/array/float64' );
var unshift = require( '@stdlib/utils/unshift' );
var arr;
var i;
arr = new Float64Array();
for ( i = 0; i < 100; i++ ) {
arr = unshift( arr, i );
}
console.log( arr );