Grunt trigger nodejs module and pass in parameter - node.js

Question

I want to write a grunt file so that when a file is added to a image folder, grunt will trigger the following nodejs image resize module GruntHandler, passing in the path to the newly added file.
Has anyone had any experience with this?
I am somewhat lost here as how to set it all up and write the grunt file to do this.
This is the code I want to trigger.
// dependencies
var async = require('async');
var gm = require('gm').subClass({ imageMagick: true });
var util = require('util');
var fs = require("fs");
var _800px = {
width: 800,
destinationPath: "large"
};
var _500px = {
width: 500,
destinationPath: "medium"
};
var _200px = {
width: 200,
destinationPath: "small"
};
var _45px = {
width: 45,
destinationPath: "thumbnail"
};
var _sizesArray = [_800px, _500px, _200px, _45px];
var len = _sizesArray.length;
// handler for dev environment
exports.GruntHandler = function (event, context) {
// Read options from the event.
console.log("Reading options from event:\n", util.inspect(event, {depth: 5}));
var srcFile = event; // file being sent by grunt ---> string url to file
var dstnFile = "/dst";
// Infer the image type.
var typeMatch = srcFile.match(/\.([^.]*)$/);
if (!typeMatch) {
console.error('unable to infer image type for key ' + srcFile);
return;
}
var imageType = typeMatch[1];
if (imageType != "jpg" && imageType != "png") {
console.log('skipping non-image ' + srcFile);
return;
}
// Download the image from S3, transform, and upload to same S3 bucket but different folders.
async.waterfall([
function download(next) {
// Read the image from local file and pass into transform.
fs.readFile(srcFile, function (err, data) {
if (err) {
next(err);
}
next(data);
});
},
function transform(response, next) {
for (var i = 0; i<len; i++) {
// Transform the image buffer in memory.
gm(response.Body, srcFile)
.resize(_sizesArray[i].width)
.toBuffer(imageType, function(err, buffer) {
if (err) {
next(err);
} else {
next(null, response.ContentType, buffer);
}
});
}
},
function upload(contentType, data, next) {
for (var i = 0; i<len; i++) {
// Stream the transformed image to a different folder.
fs.writeFile(dstnFile + "/" + _sizesArray[i].destinationPath + "/" + fileName, function (err, written, buffer) {
if (err) {
next(err);
}
});
}
}
], function (err) {
if (err) {
console.error(
'---->Unable to resize ' + srcFile +
' and upload to ' + dstnFile +
' due to an error: ' + err
);
} else {
console.log(
'---->Successfully resized ' + srcFile +
' and uploaded to ' + dstnFile
);
}
context.done();
}
);
console.log(" grunt handler called!");
};

Answer 1

You can use grunt-contrib-watch for this. Watch event should get called when new file is added (If watch doesnt work, you might be running into this https://github.com/gruntjs/grunt-contrib-watch/issues/166).
Call your function in watch event handler like following.
Use relative path of your file in place of .GruntHandler.js. In case the file is in the same directory, you can use it in the following way.
var GruntHandler = require("./GruntHandler.js").GruntHandler;
grunt.initConfig({
watch: {
scripts: {
files: ['images/*.*'],
},
},
});
grunt.event.on('watch', function(action, filepath, target) {
GruntHandler(filepath);
});