Grunt uglify : Weird behavior

I cannot figure out why uglify does not want concat string as input or output ...

This works :

uglify: {
    dev_uglify_js: {
        files: {
            'my_file.min.js': ['my_file.js']
        }
    }
}

For example, this does not works :

uglify: {
    dev_uglify_js: {
        files: {
            'my'+'_file.min.js': ['my_file.js']
        }
    }
}

Do you have any idea why ? The output error is "SyntaxError: Unexpected token".

The real insterest here is to concatenate a timestamp to the file name. But just with 2 strings it does not work so ...

Thanks for your help !

Solution

In JavaScript, an object key cannot be declared dynamically. This is not a problem with grunt or uglify - it's a language constraint.

myObject = { 'a' + 'b' : 'b' } // NOPE!

However, any object property can be accessed via square brackets. For example:

myObject = { 'banana': 'boat' }
myObject.banana // boat
myObject['banana'] // boat!

Therefore, you can add properties after the object is already created, using the square brackets syntax.

myObject = {} 
myObject[ 'a' + 'b' ] = 'b' // Yes
myObject.ab // b

The Gruntfile example

In your Gruntfile, you're bound to, at some point, call something like grunt.config.init or grunt.initConfig. This is usually done inline:

grunt.initConfig({
  uglify: {} // properties ...
});

However, initConfig simply receives an object. You can define it and manipulate it as much as you need before calling this function. So, for example:

var config = { uglify: {} };
config.uglify['such'+'dynamic'+'very'+'smarts'] = {};
grunt.initConfig(config);