How do I add javascript to a node or block

A better approach would be to get the path from Drupal, and you have to put the code in the form function;

function mymodule_form($form, &$form_state) {

... some of your forms goes here

    $form['#attached']['js'][] = drupal_get_path('module', 'mymodule') . '/myscript.js';

  return $form;

Also add your javascript between the code below

(function($)  {
  function mymodule_function(context)  {

  // from here

  // paste your code in here

  // till here

  }

  Drupal.behaviors.custommodule = {
    attach: function(context)  {
      mymodule_function(context);
    }
  }
})(jQuery);

if your script is saved as .js you can add it like that in html.tpl.php:

<?php drupal_add_js('location/of/my/script/my_script.js'); ?>

more info here

OR

<script src="location/of/my/script/my_script.js"></script> 

in your block or node body (make sure that you select format that does not filter JavaScript i.e. "PHP code")

Use function in tempale.php

Add JS file in block -

function MYTHEME_preprocess_block(&$variables) {  
    drupal_add_js(drupal_get_path('theme', 'MYTHEME') .'/mytheme.js', 'file');
} 

Add JS file in page or node -

function MYTHEME_preprocess_page(&$variables) {  
     drupal_add_js(drupal_get_path('theme', 'MYTHEME') .'/mytheme.js', 'file');

}