Add elements from one collection to the beginning of another collection.
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Add elements from one collection to the beginning of another collection.
bash
npm install @stdlib/utils-prependscript tag without installation and bundlers, use the [ES Module][es-module] available on the [esm][esm-url] branch (see [README][esm-readme]).deno][deno-url] branch (see [README][deno-readme] for usage intructions).umd][umd-url] branch (see [README][umd-readme]).javascript
var prepend = require( '@stdlib/utils-prepend' );collection to the beginning of another collection. A collection may be either an [Array][mdn-array], [Typed Array][mdn-typed-array], or an array-like [Object][mdn-object] (i.e., an [Object][mdn-object] having a valid writable length property).javascript
var arr = [ 1.0, 2.0, 3.0, 4.0, 5.0 ];
var out = prepend( 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 trueArrayBuffer][mdn-arraybuffer] may not equal the underlying [ArrayBuffer][mdn-arraybuffer] for the input collection.javascript
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 = prepend( 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 = prepend( out, [ 4.0 ] );
// returns <Float64Array>[ 4.0, 3.0, 1.0, 2.0 ]
bool = ( out.buffer === arr.buffer );
// returns falseArrayBuffer][mdn-arraybuffer]. If an [ArrayBuffer][mdn-arraybuffer] does not have enough bytes in which to store all elements, the function allocates a new [ArrayBuffer][mdn-arraybuffer] capable of holding 2^n elements, where n is the next power of 2. This procedure is similar to how environments internally handle dynamic memory allocation for [Arrays][mdn-array].ArrayBuffer][mdn-arraybuffer]. Because the function sets [ArrayBuffer][mdn-arraybuffer] bytes outside of a provided [view][mdn-typed-array], the function may overwrite bytes belonging to one or more external views. This could be a potential security vulnerability. Prefer providing [typed arrays][mdn-typed-array] which have an exclusive [ArrayBuffer][mdn-arraybuffer]; otherwise, be sure to plan for and guard against mutated state.javascript
var Float64Array = require( '@stdlib/array-float64' );
var prepend = require( '@stdlib/utils-prepend' );
var arr;
var i;
var j;
arr = new Float64Array();
for ( i = 0; i < 100; i++ ) {
j = i * 3;
arr = prepend( arr, [ j+2, j+1, j ] );
}
console.log( arr );
