Roy Truelove Roy Truelove - 1 month ago 5
Javascript Question

Grunt - resolving non-string (eg array) templates

Say I have a variable in my grunt config with an array as a value. A real world example is

from the grunt-regarde plugin, which lists all files that have changed.

I want to resolve that array using a template, so that I could (in this case) copy the changed files:

copy: {
staticWeb: {
src: '<%= grunt.regarde.changed %>',
dest: 'someDir'

gets in this case is a is a single comma delimited string instead of an array. Grunt's file processor does not parse the string, and so it cannot find the src file.

I can't remove the single quotes around the template because then it's invalid javascript.

So how do I pass that
array to the


The problem is very easy to fix once you know how, just a few lines of code, but it took me quite a while to dig up all the relevant info from the Grunt source code in order to understand what to do, so bare with me while I take you through the background ...

The general way of getting hold of a property on the configuration object is straight forward:

<%= %> // fetches grunt.config.get('')

That works for all properties that have been set on the grunt.config object, which (of course) include the config that is passed into grunt.initConfig(). This is why you can reference other tasks variables directly, such as in <%= concat.typescriptfiles.dest %>, as all the properties in the config object is in the template's own scope.

Technically this expansion happens when the (LoDash) template is passed along with either the options object (if defined) or the grunt.config object to the template processor (LoDash' template function).

So this works for values that have been set in the config itself, or by using dynamically assigned values through grunt.config.set(). See the API docs for more info.

What does not work in the same way is accessing values that are not availabe on the configuration object. It seems that for some reason I am not quite sure of, all other values always ends up as strings. This happens regardless of whether you access them directly or through method calls. For instance trying to get access to an array on the config through grunt.config.get() gets you a string.

A workaround for the problem that preserves file order

The accepted answer works in a way, but due to the globbing syntax it will be parsed by the glob() module which does not preserve file order. This was a no-no for my build.

A workaround, in case the array you want to use is not available on the config object, is to add it to the config via an intermediary task. Something like the following should work:

// This variable will be used twice to demonstrate the difference
// between directly setting an attribute on the grunt object
// and using the setter method on the grunt.config object
var myFiles = ['c/file1.txt', 'a/file2.txt', 'b/file3.txt']
module.exports = function(grunt){


        debug : {
            using_attribute: {
                src : '<%= grunt.value_as_attribute %>' // will be a string
            using_task: {
                src : '<%= value_by_setter %>' // will be an array
            no_task_direct_setter: {
                src : '<%= value_by_setter_early %>' // will be an array

    grunt.registerTask('myValSetter', function() {
        grunt.config.set('value_by_setter', myFiles );

    // a task that will report information on our set values
    grunt.registerMultiTask('debug', function(){
        grunt.log.writeln('data.src: ',;
        grunt.log.writeln('type: ', Array.isArray( "Array" : typeof;

    grunt.value_as_attribute = myFiles;

    grunt.config.set('value_by_setter_early', myFiles );

    grunt.registerTask('default',['myValSetter', 'debug']);

This will output

$ grunt
Running "myValSetter" task

Running "debug:using_attribute" (debug) task
data.src:  c/file1.txt,a/file2.txt,b/file3.txt
type:  string

Running "debug:using_task" (debug) task
data.src:  [ 'c/file1.txt', 'a/file2.txt', 'b/file3.txt' ]
type:  Array

Running "debug:no_task_direct_setter" (debug) task
data.src:  [ 'c/file1.txt', 'a/file2.txt', 'b/file3.txt' ]
type:  Array

Done, without errors.

This example is just meant to illustrate the concept, but you should be able to easily customize it to your instance :)