GitHub Jquery Ajax Progression

$.ajax({
    method: 'GET',
    url: 'data/bird.json',
    dataType: 'json',
    success: function() { },
    error: function() { },
    progress: function(e) {
        //make sure we can compute the length
        if(e.lengthComputable) {
            //calculate the percentage loaded
            var pct = (e.loaded / e.total) * 100;

            //log percentage loaded
            console.log(pct);
        }
        //this usually happens when Content-Length isn't set
        else {
            console.warn('Content Length not reported!');
        }
    }
});

Ne pas oublié dans le PHP :

header('Content-Type: application/json');
header("Content-length: $size");

où $size est la taille du fichier JSON