How to avoid unnecessary uglifying in GruntJS? - gruntjs

Question

I have a grunt file with the following definition:
uglify: {
build: {
src: 'www/temp/application.js', // a concatenation of files via grunt-contrib-concat
dest: 'www/temp/application.min.js'
}
},
what I would really like to do is to recompute the final application.min.js only in case that application.js file was changed. More precisely, I want to add the condition:
# pseudocode
if (getFileContents(application.js) == getFileContents(previously.uglified.application.js)) {
// do nothing
} else {
// run uglifying on application.js
}
Reason:
I deploy my project by git and uglifying is relatively slow (3+ seconds) and moreover, it is unnecessary since I don't change JS files often.

Answer 1

There are several possible solutions:
You can create your own grunt task that will check files for last modify time using for example fs.stat then run uglify task through grunt.task.run with prepared options as argument.
Or you can build files object dynamically passing it through filter function:
var fs = require('fs');
module.exports = function (grunt) {
function filterChanged(files) {
var mtime = '',
stats;
for (var dest in files) {
stats = fs.statSync(files[dest]);
try {
mtime = fs.readFileSync(files[dest] + '.mtime', 'utf8');
}
catch (ex) {
fs.writeFileSync(files[dest] + '.mtime', stats.mtime, 'utf8');
return files;
}
if (stats.mtime == mtime || !mtime) {
delete files[dest];
}
else {
fs.writeFileSync(files[dest] + '.mtime', stats.mtime, 'utf8');
}
}
return files;
}
grunt.initConfig({
uglify: {
build: {
files: filterChanged({
'www/temp/application.min.js': 'www/temp/application.js'
})
}
}
});
};
This causes invoke of filterChanged function every time uglify task runs.