Get the value of -webkit-transform of an element with jquery

Your matrix is a 4×4 transformation matrix:

The -770 corresponds to the v_x. To extract it, construct a WebkitCSSMatrix object:

var style = window.getComputedStyle($('#thediv').get(0));  // Need the DOM object
var matrix = new WebKitCSSMatrix(style.webkitTransform);

console.log(matrix.m41);  // -770