function move() {
var toggleMenu = document.getElementById("toggle_menu");
if (toggleMenu.style.left == "-250px") {
toggleMenu.style.left = "0px";
} else {
toggleMenu.style.left = "-250px";
}
}
<div class="slide_menu" id="toggle_menu" style="left:-250px;"> .. </div>
function move() {
var toggleMenu = document.getElementById("toggle_menu");
if (!toggleMenu.style.left || parseInt(toggleMenu.style.left) < 0) {
toggleMenu.style.left = "0px";
} else {
toggleMenu.style.left = "-250px";
}
}