how magento know which button clicked

Question

im trying to create new button in shipping multiple addresses page. When i open addresses.phtml, there's so much button like in code below.

 <div class="actions-toolbar">
        <div class="primary">
            <button type="submit" title="<?php /* @escapeNotVerified */ echo __('Go to Shipping Information') ?>" class="action primary continue<?php if ($block->isContinueDisabled()):?> disabled<?php endif; ?>" data-role="can-continue" data-flag="1"<?php if ($block->isContinueDisabled()):?> disabled="disabled"<?php endif; ?>><span><?php /* @escapeNotVerified */ echo __('Go to Shipping Information') ?></span></button>
        </div>
        <div class="secondary">
            <button type="submit" data-multiship-item-update="" class="action update" data-role="can-continue" data-flag="0"><span><?php /* @escapeNotVerified */ echo __('Update Qty &amp; Addresses') ?></span></button>
            <button type="button" title="<?php /* @escapeNotVerified */ echo __('Enter a New Address') ?>" class="action add" data-role="add-new-address"><span><?php /* @escapeNotVerified */ echo __('Enter a New Address') ?></span></button>
            <a href="<?php /* @escapeNotVerified */ echo $block->getBackUrl() ?>" class="action back"><span><?php /* @escapeNotVerified */ echo __('Back to Shopping Cart') ?></span></a>
        </div>
 </div>

And that submit will send form to AddressesPost.php which got code like below.

public function execute()
    {
        if (!$this->_getCheckout()->getCustomerDefaultShippingAddress()) {
            $this->_redirect('*/checkout_address/newShipping');
            return;
        }
        try {
            if ($this->getRequest()->getParam('continue', false)) {
                $this->_getCheckout()->setCollectRatesFlag(true);
                $this->_getState()->setActiveStep(State::STEP_SHIPPING);
                $this->_getState()->setCompleteStep(State::STEP_SELECT_ADDRESSES);
                $this->_redirect('*/*/shipping');
            } elseif ($this->getRequest()->getParam('new_address')) {
                $this->_redirect('*/checkout_address/newShipping');
            } else {
                $this->_redirect('*/*/addresses');
            }
            if ($shipToInfo = $this->getRequest()->getPost('ship')) {
                $this->_getCheckout()->setShippingItemsInformation($shipToInfo);
            }
        } catch (\Magento\Framework\Exception\LocalizedException $e) {
            $this->messageManager->addError($e->getMessage());
            $this->_redirect('*/*/addresses');
        } catch (\Exception $e) {
            $this->messageManager->addException($e, __('Data saving problem'));
            $this->_redirect('*/*/addresses');
        }
    }

Like in the code above, there's getParam() which i though that the button send data and the code getParam will know what button did we clicked. But i can't find where or when did the button send data. So my question, how could the code know which button we clicked?

Answer 1

Look inside:

vendor/magento/module-multishipping/view/frontend/web/js/overview.js

The option is:

placeOrderSubmit: 'button[type="submit"]'