funseqAsync

Function sequence.

Usage

var funseqAsync = require( '@stdlib/utils/async/function-sequence' );

funseqAsync( ...fcn )

Returns a pipeline function. Starting from the left, the pipeline function evaluates each function and passes the result as the first argument to the next function. The result of the rightmost function is the result of the whole.

function a( x, next ) {
    setTimeout( onTimeout, 0 );
    function onTimeout() {
        next( null, 2*x );
    }
}

function b( x, next ) {
    setTimeout( onTimeout, 0 );
    function onTimeout() {
        next( null, x+3 );
    }
}

function c( x, next ) {
    setTimeout( onTimeout, 0 );
    function onTimeout() {
        next( null, x/5 );
    }
}

var f = funseqAsync( a, b, c );

function done( error, result ) {
    if ( error ) {
        throw error;
    }
    console.log( result );
    // => 3
}

f( 6, done ); // ((2*x)+3)/5

The last argument provided to each function is a next callback which accepts two arguments:

  • error: error argument.
  • result: function result.

Only the leftmost function is explicitly permitted to accept multiple arguments. All other functions are evaluated as binary functions.

function a( x, y, next ) {
    setTimeout( onTimeout, 0 );
    function onTimeout() {
        next( null, (x*5) + (y*3) );
    }
}

function b( r, next ) {
    setTimeout( onTimeout, 0 );
    function onTimeout() {
        next( null, r+12 );
    }
}

var f = funseqAsync( a, b );

function done( error, result ) {
    if ( error ) {
        throw error;
    }
    console.log( result );
    // => 50
}

f( 4, 6, done );

Notes

  • The function will throw if provided fewer than 2 input arguments.
  • If a provided function calls the next callback with a truthy error argument, the pipeline function suspends execution and immediately calls the done callback for subsequent error handling.
  • 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).
  • The difference between this function and composeAsync is that this function evaluates input arguments from left-to-right, rather than right-to-left.

Examples

var funseqAsync = require( '@stdlib/utils/async/function-sequence' );

function a( x, y, next ) {
    setTimeout( onTimeout, 0 );
    function onTimeout() {
        next( null, x*y );
    }
}

function b( z, next ) {
    setTimeout( onTimeout, 0 );
    function onTimeout() {
        next( null, z+5 );
    }
}

function c( r, next ) {
    setTimeout( onTimeout, 0 );
    function onTimeout() {
        next( null, r/10 );
    }
}

var f = funseqAsync( a, b, c );

function done( error, result ) {
    if ( error ) {
        throw error;
    }
    console.log( result );
    // => 2
}

f( 5, 3, done );

See Also

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