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While a test condition is true, invoke a function for each element in a collection.
npm install @stdlib/utils-do-while-eachAlternatively,
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var doWhileEach = require( '@stdlib/utils-do-while-each' );Invokes a function for each element in a collection until either a predicate function returns false or the function has iterated over all collection elements. Note that the condition is evaluated after executing fcn; thus, fcn always executes at least once.
function predicate( value ) { return ( value === value ); } function log( value, index ) { console.log( '%s: %d', index, value ); } var arr = [ 1, 2, 3, NaN, 4 ]; doWhileEach( arr, log, predicate ); /* => 0: 1 1: 2 2: 3 3: NaN */Both the predicate function and the function to apply are provided three arguments:
- value: collection element.
- index: collection index.
- collection: input collection.
If provided an empty collection, both value and index are undefined.
function predicate( value ) { return ( value === value ); } function log( value, index ) { console.log( '%s: %s', index, value ); } var arr = []; doWhileEach( arr, log, predicate ); /* => undefined: undefined */Basic support for dynamic collections is provided. Note, however, that index incrementation is monotonically increasing.
function predicate( value ) { return ( value === value ); } function log1( value, index, collection ) { console.log( '%s: %d', index, value ); if ( index === collection.length-1 && collection.length < 10 ) { collection.push( index+2 ); } } var arr = [ 1, 2, 3, 4 ]; doWhileEach( arr, log1, predicate ); /* => 0: 1 1: 2 2: 3 3: 4 4: 5 5: 6 6: 7 7: 8 8: 9 9: 10 */ function log2( value, index, collection ) { console.log( '%s: %d', index, value ); collection.shift(); } arr = [ 1, 2, 3, 4 ]; doWhileEach( arr, log2, predicate ); /* => 0: 1 1: 3 */To set the function execution context for the applied function, provide a thisArg.
function predicate( value ) { return ( value < 3 ); } function sum( value ) { this.sum += value; this.count += 1; } var arr = [ 1, 2, 3, NaN, 4 ]; var context = { 'sum': 0, 'count': 0 }; doWhileEach( arr, sum, predicate, context ); var mean = context.sum / context.count; // returns 2.0-
A
collectionmay be either anArray,Typed Array, or an array-likeObject(excludingstringsandfunctions). -
The function returns the input
collection. -
The function does not skip
undefinedelements.function predicate( value ) { return ( value === value ); } function log( value, index ) { console.log( '%s: %s', index, value ); } var arr = [ 1, , , 4 ]; doWhileEach( arr, log, predicate ); /* => 0: 1 1: undefined 2: undefined 3: 4 */
-
The function provides limited support for dynamic collections (i.e., collections whose
lengthchanges during execution).
var isEven = require( '@stdlib/assert-is-even' ).isPrimitive; var randu = require( '@stdlib/random-base-randu' ); var floor = require( '@stdlib/math-base-special-floor' ); var doWhileEach = require( '@stdlib/utils-do-while-each' ); function predicate( value ) { return ( value === value ); } function log( value, index, collection ) { console.log( '%s: %d', index, value ); if ( isEven( index ) ) { collection.shift(); } else { collection.push( index+1 ); } } var arr; var j; var i; arr = new Array( 100 ); j = floor( randu()*arr.length ); for ( i = 0; i < arr.length; i++ ) { if ( i === j ) { arr[ i ] = NaN; } else { arr[ i ] = i; } } doWhileEach( arr, log, predicate );@stdlib/utils-do-until-each: until a test condition is true, invoke a function for each element in a collection.@stdlib/utils-do-while-each-right: while a test condition is true, invoke a function for each element in a collection, iterating from right to left.@stdlib/utils-while-each: while a test condition is true, invoke a function for each element in a collection.
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.
See LICENSE.
Copyright © 2016-2025. The Stdlib Authors.
