rect.call(zm=d3.behavior.zoom().x(x).scaleExtent([1,10]).on(zoom, draw));

After a new test i have the answer :

var currentZoom = d3.event.scale;

But only available/readable in the draw() function called by .on(zoom, draw)

rect.call( zm = d3.behavior.zoom().x(x).scaleExtent([1,10]).on(zoom, draw));



function draw() {

    // trace l'axe X

    svg.select(g.x.axis).call(xAxis);

    // trace l'axe Y

    svg.select(g.y.axis).call(yAxis);

    // trace la courbe

    svg.select(path.line).attr(d, line);



    console.log(zm.scale(), zm.translate()); // , zm.translate[1] = Y

    console.log(d3.event.scale, d3.event.translate[0]); // , d3.event.translate[1] = Y

}