TypeScript icon, indicating that this package has built-in type declarations

0.2.1 • Public • Published
About stdlib...

We believe in a future in which the web is a preferred environment for numerical computation. To help realize this future, we've built stdlib. stdlib is a standard library, with an emphasis on numerical and scientific computation, written in JavaScript (and C) for execution in browsers and in Node.js.

The library is fully decomposable, being architected in such a way that you can swap out and mix and match APIs and functionality to cater to your exact preferences and use cases.

When you use stdlib, you can be absolutely certain that you are using the most thorough, rigorous, well-written, studied, documented, tested, measured, and high-quality code out there.

To join us in bringing numerical computing to the web, get started by checking us out on GitHub, and please consider financially supporting stdlib. We greatly appreciate your continued support!


NPM version Build Status Coverage Status

Add elements from one collection to the beginning of another collection.


npm install @stdlib/utils-prepend


var prepend = require( '@stdlib/utils-prepend' );

prepend( collection1, collection2 )

Adds elements from one collection to the beginning of another 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 = 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 true

Note that the function returns the extended collection. 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 = 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 false


  • The function adds elements to a typed array by setting values in the underlying ArrayBuffer. If an ArrayBuffer does not have enough bytes in which to store all elements, the function allocates a new 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.
  • Beware when providing typed arrays which are views pointing to a shared (or pooled) ArrayBuffer. Because the function sets ArrayBuffer bytes 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 exclusive ArrayBuffer; otherwise, be sure to plan for and guard against mutated state.


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 );

See Also


This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.






Copyright © 2016-2024. The Stdlib Authors.

Package Sidebar


npm i @stdlib/utils-prepend



Weekly Downloads






Unpacked Size

47.5 kB

Total Files


Last publish


  • stdlib-bot
  • kgryte
  • planeshifter
  • rreusser