Retrieving output from Node script in a Grunt task

问题

I'm fairly new to Grunt, so this might be quite a basic question. I've got a Gruntfile.js that looks like this:

/*global module:false*/ 
module.exports = function (grunt) { 

  grunt.initConfig({ 

  }); 

  grunt.registerTask('default', 'measureText'); 

  grunt.registerTask('measureText', 'Measures size of text', function() { 
    grunt.log.writeln('========================================================================'); 
    grunt.log.writeln('= output of ImageMagick should be on next line:                        ='); 
    var im = require("node-imagemagick"); 

    im.identify(['-format', '%wx%h', 'build/text.png'], function(err, output){ 
      if (err) throw err; 
      console.log('dimension: '+output);  // <-- NOTHING WRITTEN!
    }); 

    grunt.log.writeln('========================================================================'); 
    return; 
  });    
};

As you can see, it's calling the node-imagemagick method identify to get the width and height of an image (build/text.png). When I run my grunt script above, there is no output from the identify() callback. (That's the console.log line above).

Yet if I create a Node script (e.g. test-node-imagemagick.js) to test that same code, it works just fine, e.g.

#!/usr/bin/env node

var im = require("node-imagemagick");
im.identify(['-format', '%wx%h', 'build/text.png'], function(err, output){
  if (err) throw err;
  console.log('dimension: '+output);
});

So how do I call Node packages from within Grunt tasks, and get returned values?

By the way, I did install the package by doing:

$ npm install node-imagemagick

... from the directory that contains the Gruntfile.js.

Thanks!

回答1:

Edit:

The reason your task never completes is because of your ambiguous return at the end:

return; <---

You are disrupting the async call to:

im.identify(function(){
  //do async
})

return; //exit task

Try this:

grunt.registerTask('measureText', function(done) {
    //omitting code

    im.identify(function(){
       //do async stuff

       done()
    })
})

The function argument done() tells the task runner that it should finish after you do something asynchronous instead of ending before any of that code executes.

Original:

Your requires looks very different in each of those scripts.

require('imagemagick')

--- vs ---

require('node-imagemagick')

Grunt is probably swallowing the error

Also, I think its just:

npm install imagemagick

回答2:

I just found the answer by some more digging, here: Using a node module within a Grunt Task fails

Basically, my Grunt task has to be asynchronous if it is to receive a callback:

/*global module:false*/ 
module.exports = function (grunt) { 
  var im = require("node-imagemagick"); 


  grunt.initConfig({ 
  }); 

  grunt.registerTask('default', 'measureText'); 

  grunt.registerTask('measureText', 'Measures size of text', function() { 
    var done = this.async(); // <-- Make the task asynchronous!
    grunt.log.writeln('========================================================================'); 
    grunt.log.writeln('= output of ImageMagick should be on next line:                        ='); 

    im.identify(['-format', '%wx%h', 'build/text.png'], function(err, output){ 
      if (err) throw err; 
      console.log('dimension: '+output); 
      done();
    });  
  });    
};

Of course, that means that the output would not actually appear between the two lines of equals signs, if I'd kept the second line there.

回答3:

Doing some more research I was able to get this to work. First off, I would switch to this library which was recommended by the imagemagick developer README.

https://github.com/aheckmann/gm

But, that is up to you if you want to use an unmaintained library.

Anyway here it is:

grunt.registerTask('measureText', function(done) {
  //omitting code

  var done = this.async() //create async task

  im.identify('/path/to/image', function(err, output){
   //do async stuff
   console.log('dimension: %s', output)
   done()
  })

  //or use gm
  gm('/path/to/image')
   .size(function(err, size) {
      console.log('gm size: %s', size)
      done()
   })
})

来源：https://stackoverflow.com/questions/28597314/retrieving-output-from-node-script-in-a-grunt-task

标签

node.js

gruntjs

node-imagemagick