To debug JavaScript in a web page, start in the browser’s Developer Tools Console: find the first relevant error and its file-and-line link, then open that location in the source debugger, set a breakpoint, and inspect the values, scope, and call stack as the code runs. The Console is best for errors and quick checks; the debugger is best for finding where execution first goes wrong.
Start with the Console
Open your browser’s Developer Tools and select the Console. The exact menu path and panel layout vary by browser, so use the browser’s current menu or official help if you need a shortcut.
- Reproduce the problem, such as by reloading the page or repeating the action that triggers the behavior.
- Look for the first error that appears to relate to the problem. Read the message and note the linked script file and line number, when provided. Error wording and presentation vary by browser.
- Click the file-and-line reference to open the corresponding code in the debugger.
The Console can also evaluate JavaScript in the context of the loaded page. Use it to check a small expression or inspect current page state—for example, document.title to read the page title. Treat console expressions as diagnostic checks: they show the current state, but do not by themselves explain how the page reached it.
Pause execution with a breakpoint
Chrome calls its source debugger Sources; Firefox calls it Debugger. Panel names and layouts differ across browsers, but the basic workflow is the same: open the referenced script, choose a line near the suspected failure, and set a breakpoint. A breakpoint pauses execution when the code reaches that line.
#1 Best Overall
- Read Before You Buy — No Video Output: These adapters support charging and USB 2.0 data transfer, but cannot transmit video signals. Except for standard USB webcams (which use USB data only), they are not compatible with HDMI/DisplayPort cables, video-capable USB-C hubs, or docking stations with video output.
- Convert USB-A Ports to USB-C: Designed to connect USB-C earphones, cables, flash drives, card readers, and other USB-C accessories to standard USB-A ports. Plug-and-play with no drivers or software required.
- Aluminum Alloy Housing: Built with a sturdy aluminum alloy shell that aids in heat dissipation and protects against daily wear and scratches. Designed to maintain a stable and secure connection.
- Compact & Travel-Friendly: The ultra-compact design allows the adapter to stay plugged into your device without blocking adjacent ports or adding bulk, reducing wear and tear on your original USB ports.
- 12-Month Warranty: Backed by a 12-month manufacturer warranty for peace of mind. Designed to meet strict quality control standards for reliable everyday performance.
- In the debugger, open the script identified by the Console error.
- Set a breakpoint on the failing statement or a nearby line that runs before it.
- Reload the page or repeat the action that triggers the code.
- When execution pauses, inspect the current values and compare them with what the code expects.
- Step through the next statements to identify where the actual behavior first diverges from the expected behavior.
Read the paused state
- Variables and scope: Check the values available at the paused line, including local variables and values from surrounding scopes. A value that is missing, stale, or a different type than expected can reveal the source of the failure.
- Call stack: Follow the functions that led to the paused line. This helps distinguish a faulty statement from an unexpected caller or execution path.
- Stepping: Advance one statement at a time and watch which value changes immediately before the result goes wrong.
For example, if a click handler fails while reading a property from an object, pause before that read. Check whether the object exists and has the expected shape, then step forward to see whether the failing expression is reached with different data than anticipated.
Use debugger; when a line breakpoint is awkward
You can add a debugger; statement at the point where you want execution to pause:
Rank #2
- 5-in-1 USB-C Hub: Experience comprehensive connectivity featuring a Power Delivery input, two USB-A 2.0 ports, a USB-A 3.0 port, and an HDMI port. (Note: The USB-C power delivery input port is only for connecting an external wall charger to power your laptop and cannot power peripheral devices.)
- 90W Pass-Through Charging: Achieve optimal charging with 90W pass-through power to your laptop, supported by a total input of 100W, with the hub reserving 10W for operational efficiency. (Note: Wall charger not included.)
- Quick Data Transfers: Accelerate your productivity with rapid data transfers using a high-speed 5Gbps USB 3.0 port and two 480Mbps USB 2.0 ports.
- 4K HDMI Display: Enhance your visual experience with a hub capable of delivering 4K resolution at 30Hz in both mirror and extend modes. Please note that this hub is compatible with MacBook (macOS 12 and newer), Windows 10 and 11, ChromeOS, and laptops equipped with DP Alt Mode and Power Delivery. Note: This device is not compatible with Linux.
- What You Get: Anker USB-C Hub (5-in-1, 4K HDMI), welcome guide, 18-month warranty, and our friendly customer service.
function updateTotal(items) {
debugger;
return items.reduce((sum, item) => sum + item.price, 0);
}When debugging functionality is available, the statement can pause execution like a breakpoint. MDN describes it this way: “The debugger statement invokes any available debugging functionality, such as setting a breakpoint.” MDN’s debugger reference notes that it has no effect when no debugging functionality is available. Remove the statement after diagnosing the issue, or leave it only when the pause is intentional.
Debug bundled or minified code with source maps
When the deployed script is bundled or minified, its lines and names may not resemble the source you wrote. A working source map lets DevTools connect debugging activity in the deployed file to the original source. Chrome documents this in its source maps guide.
What’s actually slowing this PC down?
Pick the symptom - the matching free tool is one click away.
Rank #3
- Sleek 7-in-1 USB-C Hub: Features an HDMI port, two USB-A 3.0 ports, and a USB-C data port, each providing 5Gbps transfer speeds. It also includes a USB-C PD input port for charging up to 100W and dual SD and TF card slots, all in a compact design.
- Flawless 4K@60Hz Video with HDMI: Delivers exceptional clarity and smoothness with its 4K@60Hz HDMI port, making it ideal for high-definition presentations and entertainment. (Note: Only the HDMI port supports video projection; the USB-C port is for data transfer only.)
- Double Up on Efficiency: The two USB-A 3.0 ports and a USB-C port support a fast 5Gbps data rate, significantly boosting your transfer speeds and improving productivity.
- Fast and Reliable 85W Charging: Offers high-capacity, speedy charging for laptops up to 85W, so you spend less time tethered to an outlet and more time being productive.
- What You Get: Anker USB-C Hub (7-in-1), welcome guide, 18-month warranty, and our friendly customer service.
If the original source does not appear, check that the deployed script points to a source map and that the map is available to the browser. Without an accessible map, you may need to inspect the deployed script instead; a source map cannot help if it is missing or unavailable.
When the Console is enough—and when to switch panels
| Tool | Use it for |
|---|---|
| Console | Reading runtime errors, following a reported file-and-line reference, and evaluating small expressions against the loaded page. |
| Source debugger | Pausing execution, stepping through statements, and inspecting values, scope, and the call stack. |
Use the Console to find a starting point, then switch to the debugger when you need to understand the execution path or the values at the moment of failure. This pairing is more informative than repeatedly reloading and reading the same error.
Rank #4
- Dual Converters, Infinite Potential：Includes 2× USB C male to USB A female adapters and 2× USB A male to USB C female adapters. Perfect for a wide range of uses—tablets with Bluetooth keyboards, expand USB ports on macbook, and more. Two different converters for all your daily needs
- Next-Level 10Gbps & 3A Charging: No more slow 480Mbps, this usb to usb c adapter has a transfer speed of up to 10Gbps, allowing you to do more transferring in less time. This usb adapter fits both USB A and USB C charger, supporting up to 3A fast charging
- Upgraded Exquisite Craftsmanship: With an aluminum alloy housing and metal connector, the usbc to usb adapter is extremely durable and sturdy. Rigorously tested to withstand more than 10,000 times of plugging and unplugging, ensuring long-lasting performance
- Broad Compatible: The usb c to usb adapter widely supports all USB C/ USB A devices like laptops, tablets, cellphones, car chargers, and phone chargers. Such as compatible with MacBook Pro/Air 2023/2022, Thunderbolt 4/3 Devices,Apple MagSafe Watch 9/8/7/SE/Ultra, iPad Pro 2022/2021, Samsung Galaxy S23/S20/S10, and iPhone 17/16/15 Pro. Plug and play
- Please Note: To reach 10Gbps speed, keep the cable under 3.3 ft. For USB A Male to USB C adapters, try flipping the USB C connector. USB C Male to USB A adapters support bidirectional 10Gbps transfer within 3.3 ft
Common debugging problems and fixes
- No useful error appears: Reproduce the behavior while watching the Console, then set a breakpoint in the code that should run. A breakpoint can show whether execution reaches that code and what state it has at that point.
- The error points to a minified file: Check whether a source map is linked and accessible. If DevTools cannot map to the original source, debug the deployed file or make the map available.
- The breakpoint does not pause: Confirm it is set on executable code, then reload or repeat the action that reaches that code. If the code path is difficult to target with a line breakpoint, add
debugger;at the desired point and try again. - A value looks correct in the Console but the bug remains: A console expression shows the page’s current state, not necessarily the state at the time of failure. Pause at the relevant statement and inspect the value there.
- You cannot find the same panel name: Browser interfaces differ. Look for that browser’s source-debugging panel; Chrome uses Sources and Firefox uses Debugger.
Or skip the browser setup
If your task is to capture a page rather than diagnose its JavaScript, ScreenshotNeo offers a one-request screenshot API. It is separate from browser debugging and does not replace the Console or debugger when you need to inspect code.
Quick Recap
Best Value
- 5-in-1 Connectivity: Equipped with a 4K HDMI port, a 5 Gbps USB-C data port, two 5 Gbps USB-A ports, and a USB C 100W PD-IN port. Note: The USB C 100W PD-IN port supports only charging and does not support data transfer devices such as headphones or speakers.
- Powerful Pass-Through Charging: Supports up to 85W pass-through charging so you can power up your laptop while you use the hub. Note: Pass-through charging requires a charger (not included). Note: To achieve full power for iPad, we recommend using a 45W wall charger.
- Transfer Files in Seconds: Move files to and from your laptop at speeds of up to 5 Gbps via the USB-C and USB-A data ports. Note: The USB C 5Gbps Data port does not support video output.
- HD Display: Connect to the HDMI port to stream or mirror content to an external monitor in resolutions of up to 4K@30Hz. Note: The USB-C ports do not support video output.
- What You Get: Anker 332 USB-C Hub (5-in-1), welcome guide, our worry-free 18-month warranty, and friendly customer service.
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webpSee the ScreenshotNeo API documentation for request options. ScreenshotNeo accepts cookie or consent banners and removes more than 60 known consent platforms, newsletter popups, and chat widgets before capture; each of those steps can be turned off. Bot checks, blank pages, timeouts, failed loads, and cache hits are not billed, and responses identify the page verdict and billing status in headers. Its MCP server provides screenshot tools for AI agents, and the free plan includes 1,000 screenshots a month with no card; paid plans start at $5 for 3,000. Sign up for ScreenshotNeo’s free plan.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
