Anonymous state retaining event listener

gistfile1.js

document.addEventListener(
    "mousemove",
    function (e) {
        var sample = {x: parseInt(e.clientX, 10) || 0, y: parseInt(e.clientY, 10) || 0};
        var diff = {x: sample.x - this.lastSample.x, y: sample.y - this.lastSample.y};

        this.lastSample = sample;
        console.dir(diff);
    }.bind({lastSample: {x: 0, y: 0}}),
    false
    );