Web Inspector ReferenceDOM Breakpoints

DOM Breakpoints can be useful when debugging DOM modifications in JavaScript. They are set by right-clicking on any DOM node preview or link, such as the DOM tree in the Elements Tab, and choosing one of the items in the Break on submenu.

Once a DOM Breakpoint has been added, it will be shown in both the Elements Tab and Sources Tab, and can be enabled/disabled/removed from both. Just like in the Sources Tab, clicking on [DOM Breakpoint] in the Elements Tab will toggle the DOM Breakpoint‘s enabled/disabled state.


If a DOM Breakpoint has been added to a child DOM node, and one of the ancestor/parent DOM nodes is collapsed in the DOM tree, [Descendant DOM Breakpoint] is shown in the Elements Tab. Right-clicking on it (or anywhere on the associated DOM node) will show options to Enable Descendant Breakpoints / Disable Descendant Breakpoints, Delete Descendant Breakpoints, and Reveal Descendant Breakpoints.

DOM Breakpoints are preserved between Web Inspector sessions, but they are only re-added if a DOM node that matches the tag path (i.e. tag name and index within the parent node all the way to the root) of that DOM Breakpoint exists in the current page (e.g. a DOM Breakpoint with the tag path body > div:nth-child(2) wouldn’t be shown if the second child of the <body> was not a <div>).

DOM Breakpoints have three different types: Subtree Modified, Attribute Modified, and Node Removed.

Subtree Modified

DOM Breakpoints of this type will pause JavaScript execution whenever any DOM node is added/removed to the subtree of the associated DOM node.

This is not limited to immediate descendants, however, so setting a Subtree Modified DOM Breakpoint on the <body> will pause JavaScript execution every time any DOM node is added/removed from any descendant of the <body>.

Attribute Modified

DOM Breakpoints of this type will pause JavaScript execution whenever any attribute is modified on the associated DOM node.

This includes when new attributes are added (e.g. setAttribute), and when existing attributes are completely removed (e.g. removeAttribute).

Node Removed

This DOM Breakpoint is very straightforward, in that it will pause JavaScript execution if the associated DOM node is removed from the DOM tree.

This includes when an ancestor of the associated DOM node is removed from the DOM tree as well.

Node Removed DOM Breakpoints entirely “consume” Subtree Modified DOM Breakpoints set on an ancestor DOM node, meaning that any Subtree Modified DOM Breakpoints set on any ancestor DOM nodes will not fire.

State

DOM Breakpoints can either be enabled or disabled . Ideally, DOM Breakpoints will always be enabled , but there are a few reasons why they would be disabled :

  • the DOM Breakpoint was manually disabled . Clicking (or right-clicking and selecting Enable Breakpoint or Disable Breakpoint in the context menu) on any breakpoint icon in the navigation sidebar in the Sources Tab will toggle between enabled and disabled .
  • breakpoints have been globally disabled . The global breakpoint control is a button that looks just like a breakpoint located in the top of the navigation sidebar in the Sources Tab.

All enable/disable/delete toggles are available in the context menu when right-clicking on any DOM Breakpoint.

Icon legend:

  • enabled (breakpoints globally enabled)
  • disabled (breakpoints globally enabled)
  • enabled (breakpoints globally disabled)
  • disabled (breakpoints globally disabled)

Written January 14, 2020 by Devin Rousso

Last updated August 10, 2020 by Devin Rousso