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Add elements from one collection to the beginning of another collection.
import prepend from 'https://cdn.jsdelivr.net/gh/stdlib-js/utils-prepend@esm/index.mjs';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 trueNote 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.
import ArrayBuffer from 'https://cdn.jsdelivr.net/gh/stdlib-js/array-buffer@esm/index.mjs'; import Float64Array from 'https://cdn.jsdelivr.net/gh/stdlib-js/array-float64@esm/index.mjs'; 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 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.
<!DOCTYPE html> <html lang="en"> <body> <script type="module"> import Float64Array from 'https://cdn.jsdelivr.net/gh/stdlib-js/array-float64@esm/index.mjs'; import prepend from 'https://cdn.jsdelivr.net/gh/stdlib-js/utils-prepend@esm/index.mjs'; 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 ); </script> </body> </html>@stdlib/utils-append: add elements from one collection to the end of another collection.@stdlib/utils-unshift: add one or more elements to the beginning of a collection.
This package is part of stdlib, a standard library 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.
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