trythen

If a function does not throw, return the function return value; otherwise, return the return value of a second function.

Usage

var trythen = require( '@stdlib/utils/try-then' );

trythen( x, y )

If a function x does not throw, returns the return value of x; otherwise, returns the return value of a second function y.

function x1() {
    return 1.0;
}

function x2() {
    throw new Error( 'beep' );
}

function y() {
    return -1.0;
}

var z = trythen( x1, y );
// returns 1.0

z = trythen( x2, y );
// returns -1.0

The function y is provided a single argument:

• error: the error thrown by x.

var randu = require( '@stdlib/random/base/randu' );

function x() {
    if ( randu() < 0.5 ) {
        throw new Error( 'beep' );
    }
    throw new TypeError( 'boop' );
}

function y( err ) {
    if ( err instanceof TypeError ) {
        return 'boops';
    }
    return 'beeps';
}

var z = trythen( x, y );
// returns <string>

Examples

var randu = require( '@stdlib/random/base/randu' );
var ceil = require( '@stdlib/math/base/special/ceil' );
var repeatString = require( '@stdlib/string/repeat' );
var trythen = require( '@stdlib/utils/try-then' );

var z;
var i;

function x() {
    if ( randu() < 0.9 ) {
        throw new Error( 'BOOP' );
    }
    return repeatString( 'BOOP', ceil( randu()*3.0 ) );
}

function y() {
    return repeatString( 'beep', ceil( randu()*5.0 ) );
}

for ( i = 0; i < 100; i++ ) {
    z = trythen( x, y );
    console.log( z );
}

---

See Also

• @stdlib/utils/try-catch: if a function does not throw, return the function return value; otherwise, return y.
• @stdlib/utils/async/try-then: if a function does not return an error, invoke a callback with the function result; otherwise, invoke a second function.