doWhileAsync

Invoke a function while a test condition is true.

Installation

npm install @stdlib/utils-async-do-while

Usage

var doWhileAsync = require( '@stdlib/utils-async-do-while' );

doWhileAsync( fcn, predicate, done[, thisArg ] )

Invokes a function until a predicate function returns false. Note that the predicate function is evaluated after executing fcn; thus, fcn always executes at least once.

function fcn( i, next ) {
    setTimeout( onTimeout, 0 );
    function onTimeout() {
        console.log( 'beep: %d', i );
        next();
    }
}

function predicate( i, clbk ) {
    clbk( null, i < 5 );
}

function done( error ) {
    if ( error ) {
        throw error;
    }
}

doWhileAsync( fcn, predicate, done );
/* =>
    beep: 0
    beep: 1
    beep: 2
    beep: 3
    beep: 4
*/

The function to invoke is provided two arguments:

• i: iteration number (starting from zero)
• next: a callback which must be invoked before proceeding to the next iteration

The predicate function is provided two arguments:

• i: iteration number (starting from one)
• clbk: a callback indicating whether to invoke fcn

The clbk function accepts two arguments:

• error: error object
• bool: test result

If the test result is truthy, the function continues invoking fcn; otherwise, the function invokes the done callback.

The first argument of both clbk and next is an error argument. If either function is called with a truthy error argument, the function suspends execution and immediately calls the done callback for subsequent error handling.

function fcn( i, next ) {
    setTimeout( onTimeout, 0 );
    function onTimeout() {
        next( new Error( 'beep' ) );
    }
}

function predicate( i, clbk ) {
    clbk( null, i < 5 );
}

function done( error ) {
    console.error( error.message );
    // => beep
}

doWhileAsync( fcn, predicate, done );

The done callback is invoked with an error argument and any arguments passed to the final next callback.

function fcn( i, next ) {
    setTimeout( onTimeout, 0 );
    function onTimeout() {
        next( null, i );
    }
}

function predicate( i, clbk ) {
    clbk( null, i < 5 );
}

function done( error, result ) {
    if ( error ) {
        throw error;
    }
    console.log( result );
    // => 4
}

doWhileAsync( fcn, predicate, done );

To set the function execution context for the invoked function, provide a thisArg.

function fcn( i, next ) {
    this.count += 1;
    setTimeout( onTimeout, 0 );
    function onTimeout() {
        next();
    }
}

function predicate( i, clbk ) {
    clbk( null, i < 5 );
}

var context = {
    'count': 0
};

doWhileAsync( fcn, predicate, done, context );

function done( error ) {
    if ( error ) {
        throw error;
    }
    console.log( context.count );
    // => 5
}

Notes

• Execution is not guaranteed to be asynchronous. To guarantee asynchrony, wrap the done callback in a function which either executes at the end of the current stack (e.g., nextTick) or during a subsequent turn of the event loop (e.g., setImmediate, setTimeout).

Examples

var repeatString = require( '@stdlib/string-repeat' );
var doWhileAsync = require( '@stdlib/utils-async-do-while' );

function fcn( i, next ) {
    setTimeout( onTimeout, 0 );
    function onTimeout() {
        next( null, repeatString( 'beep', i+1 ) );
    }
}

function predicate( i, clbk ) {
    setTimeout( onTimeout, 0 );
    function onTimeout() {
        clbk( null, i < 5 );
    }
}

function done( error, result ) {
    if ( error ) {
        throw error;
    }
    console.log( result );
}

doWhileAsync( fcn, predicate, done );

See Also

• @stdlib/utils-async/do-until: invoke a function until a test condition is true.
• @stdlib/utils-do-while: invoke a function while a test condition is true.
• @stdlib/utils-async/until: invoke a function until a test condition is true.
• @stdlib/utils-async/while: invoke a function while a test condition is true.

Notice

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.

Community

License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.