WooCommerce progress bar from cart contents total value

My aiming result is like this:

With the current code its not showing the cart total in the progress bar. What am I doing wrong? And how can I integrate those steps/stacks?

var carttotal = WC()->cart->get_cart_contents_total(); 
document.getElementById("cart-progress-bar").value = carttotal;

#cart-progress-bar {
  background-color: #f9f9f9;
  box-shadow: inset 0 1px 1px rgba(100, 100, 100, 0.1);
  box-sizing: initial;
  color: #fff;
  font-size: 20px;
  height: 30px;
  position: relative;
  text-align: center;
  width: auto;
  margin: 10px;
  border:1px solid grey;
}

<progress id="cart-progress-bar" max="100" value="0"></progress>

Answer

Your example didn’t state exactly where you wanted this. I’ve added it to the cart page via the woocommerce_before_cart_table action hook. Which would look like this after adding some extra CSS styling.

You could also add this to a template file of course without the add_action/function mark up.

Action hook:

add_action( 'woocommerce_before_cart_table', 'cart_discount_progress_bar' );
function cart_discount_progress_bar() {

    // Create progress bar
    $cart_total = WC()->cart->get_cart_contents_total() + WC()->cart->get_cart_contents_tax();
    printf( '<progress id="cart-progress-bar" max="100" value="%s"></progress>', $cart_total );

    // Create steps
    $steps = array(
        0 => '',
        30 => __( '3% discount', 'discount-bar'), 
        50 => __( '8% discount', 'discount-bar'), 
        100 => __( '10% discount', 'discount-bar'), 
    );
    echo '<div id="cart-progress-steps">';
    foreach ( $steps as $step => $discount ) {
        printf('<div class="step step-%1$s" style="left:%1$s%%">%2$s<span class="discount">%3$s</span></div>', $step, wc_price( $step ), $discount );
    }
    echo '</div>';

}

CSS:

.woocommerce-cart #cart-progress-bar {
    border-radius:0;
    border: 1px solid #eaeaea;
    margin-top: 1em;
    color: cornflowerblue;
    background: floralwhite;
}

.woocommerce-cart #cart-progress-bar::-webkit-progress-value {
    background: cornflowerblue;
}

.woocommerce-cart #cart-progress-bar::-webkit-progress-bar {
    background: floralwhite;
}

.woocommerce-cart #cart-progress-steps {
    margin-bottom: 3em;
}

.woocommerce-cart #cart-progress-bar,
.woocommerce-cart #cart-progress-steps {
    width: 100%;
    position: relative;
    height: 20px;
    box-sizing: border-box;
}

.woocommerce-cart #cart-progress-steps .step {
    position: absolute;
    width: 70px;
    height: 20px;
    font-size: 14px;
    text-align: center;
    transform: translateX(-50%);
}

.woocommerce-cart #cart-progress-steps .step .discount {
    font-size: 12px;
    line-height: 11px;
    display: block;
}

.woocommerce-cart #cart-progress-steps .step:before {
    content: '';
    display: block;
    position: absolute;
    width: 40px;
    height: 18px;
    border-left: 2px solid black;
    left: 50%;
    top: -26px;
}

The mistake in your example was that you were trying to use PHP to create a value for a JavaScript variable. So to make that work you would either have to jump in and out of PHP:

var carttotal = <?php echo WC()->cart->get_cart_contents_total() + WC()->cart->get_cart_contents_tax(); ?>;

Or choose to build your whole progress bar in PHP like in my example.