make exec function inside forEach do one by one

I'm getting stuck in problem with asynchronous of nodejs. I want to resize on images in folder, resize is an executable binary file. The problem is my resize cannot be executed multiple times at same time. so that I use Array.prototype.forEach instead of async.forEach to expect that each file will be processed one by one.

var exec  = require('child_process').exec;

exec('ls ' + IMAGE_FOLDER, function (error, stdout, stderr) {
    if (error) {throw error;}
    var fileList = stdout.split("\n");
    fileList.pop();  //Remove the last element that null
    fileList.forEach(function(imageFile, index, array) {
        var inFile = IMAGE_FOLDER + imageFile;
        console.log(inFile);
        exec('resize ' +  inFile, function(err, stdout, stderr){
            if (err) {
                console.log(stderr);
                throw err;
            }
            console.log('resized ' + imageFile );
        })
    });
});

But the result I got is the behavior of my code is none-block, it prints out:

image1 
image2
...
resized image1
resized image2
...

I expected the behavior of printout should be:

image1
resize image1
image2
resize image2
...

Please show me where I was wrong. Any help is vary appreciate.

via Ngoan Tran