gruntjs - Getting undefined with custom function execution in grunt task -

try execute below custom task:

'use strict'; module.exports = function(grunt) {     grunt.initconfig({          log: {             one: [1, 2, 3],             two: "hello world",             three: true,             four: {                 five: function() {                     grunt.log.writeln("hi");                 },                 six: function() {                     grunt.log.writeln("welcome");                 }             }         }      });     grunt.registermultitask('log', 'log stuff', function() {         grunt.log.writeln(this.target + ": " + this.data + "\n");          if (this.target === 'four') {             console.log(this.data);              for(var d in this.data) {                 console.log(this.data['five']());                  console.log(this.data['six']());             }         }     });      grunt.registertask('default', 'log'); }; 

i getting below output:

running "log:one" (log) task one: 1,2,3  running "log:two" (log) task two: hello world  running "log:three" (log) task three: true  running "log:four" (log) task four: [object object]  { five: [function], six: [function] } hi undefined welcome undefined hi undefined welcome undefined  done, without errors. 

i not able understand while executing function 5 , six; displaying correct output "undefined". undefined comes ?

when write console.log(this.data['five']()); means "print out return value of function defined @ this.data.five, is:

function() {     grunt.log.writeln("hi"); }  

this function has no explicit return, return value undefined, , code prints out. avoid this, change code to:

for(var d in this.data) {     this.data['five']();     this.data['six'](); } 

or better, avoid duplication:

for(var d in this.data) {     this.data[d](); }