Waterfall

Execute functions in series, passing the results of one function as arguments to the next function.

Usage

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

waterfall( fcns, clbk[, thisArg] )

Executes functions in series, passing the results of one function as arguments to the next function.

function foo( next ) {
    next( null, 'beep' );
}

function bar( str, next ) {
    console.log( str );
    // => 'beep'

    next();
}

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

var fcns = [ foo, bar ];

waterfall( fcns, done );

To set the this context for all functions in the provided function array, provide a thisArg.

function foo( next ) {
    this.idx = 0;
    next( null, 'beep' );
}

function bar( str, next ) {
    this.idx += 1;
    console.log( str );
    // => 'beep'

    next();
}

function done( error ) {
    if ( error ) {
        throw error;
    }
    console.log( ctx.idx );
    // => 1
}

var ctx = {};
var fcns = [ foo, bar ];

waterfall( fcns, done, ctx );

waterfall.factory( fcns, done[, thisArg] )

Returns a reusable waterfall function.

function foo( next ) {
    next( null, 'beep' );
}

function bar( str, next ) {
    console.log( str );
    // => 'beep'

    next();
}

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

var fcns = [ foo, bar ];

var run = waterfall.factory( fcns, done );

run();
run();
run();

Notes

  • The last argument applied to each waterfall function is a callback. The callback should be invoked upon a series function completion. The first argument is reserved as an error argument (which can be null). Any results which should be passed to the next function in the series should be provided beginning with the second argument.
  • If any function calls the provided callback with a truthy error argument, the waterfall suspends execution and immediately calls the done callback for subsequent error handling.
  • This implementation does not guarantee that execution is asynchronous. To do so, 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 replace = require( '@stdlib/string/replace' );
var waterfall = require( '@stdlib/utils/series-waterfall' );

function foo( next ) {
    next( null, 'beep' );
}

function bar( str, next ) {
    console.log( str );
    next( null, replace( str, 'e', 'o' ) );
}

function fun( str, next ) {
    console.log( str );
    next();
}

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

var fcns = [ foo, bar, fun ];

waterfall( fcns, done );