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For a value already known to be a string, read text.length. It returns the string’s length in UTF-16 code units—not always the number of characters a person sees. If a value might not be a string, check it with typeof before reading .length.
Get the length of a string
Use the length property on the string value:
function getStringLength(text: string): number {
return text.length;
}
The parameter uses TypeScript’s primitive string type, and the function returns a number. TypeScript builds on JavaScript, so string values use JavaScript’s length behavior. See the TypeScript overview for JavaScript programmers.
Check a value before reading its length
If a value is typed as unknown, first establish at runtime that it is a string. TypeScript narrows the value inside the checked branch:
function checkedStringLength(value: unknown): number | undefined {
if (typeof value === "string") {
return value.length;
}
return undefined;
}
This example returns undefined for a non-string. If that is not appropriate for your API, return a validation error or use a discriminated result instead. A type assertion such as value as string does not check the runtime value; it only tells the type checker to treat it as a string. Keep validation and measurement as separate steps.
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#1 Best Overall
Elebase USB to USB C Adapter for iPhone 18 Pro Max,USBC Car Charger Adapter
- 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.
Know what “length” counts
JavaScript’s string .length counts UTF-16 code units. That is the right choice when your required limit is defined in those units, but it is not a universal count of Unicode code points or user-perceived characters. The MDN reference for String.length explains the distinction.
| Counting method | What it counts | When to use it |
|---|---|---|
text.length |
UTF-16 code units; a supplementary code point such as 😄 counts as two. | When the API or your limit specifies UTF-16 code units. |
[...text].length |
Unicode code points; a surrogate pair is one item, but combining marks and joined emoji remain separate code points. | When you need a simple code-point count. |
Intl.Segmenter with granularity: "grapheme" |
Grapheme clusters, a closer approximation of user-perceived characters. | When the counting rule is based on displayed character clusters. |
Count UTF-16 code units
const units = "😄".length; // 2
Count Unicode code points
const codePoints = [..."😄"].length; // 1
Spreading a string iterates its code points, so it treats a surrogate pair as one item. It does not combine multiple code points into a single displayed character.
Rank #2
Anker USB-C Hub, 5-in-1 USB Hub for Laptops, 4K HDMI Multiport Adapter
- 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.
Count grapheme clusters
const segmenter = new Intl.Segmenter(undefined, { granularity: "grapheme" });
const graphemes = Array.from(segmenter.segment(text)).length;
Grapheme segmentation is closer to what people perceive as characters. For example, MDN shows the family emoji "👨👩👧👧" as one grapheme cluster even though it consists of multiple code points and code units. Check your target runtime’s support for Intl.Segmenter, and follow the exact counting rule your product requires.
Quick Recap
Bestseller No. 5
Best Value
Anker USB C Hub, 5-in-1 USBC to HDMI Splitter with 4K Display
- 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.
Rank #4
Sale
UGREEN USB to USB C Adapter Combo 4-Pack, 10Gbps USB C Converter Space Gray
- 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
Rank #3
Sale
Anker USB C Hub, 7in1 Multi-Port USB Adapter, 4K@60Hz USBC to HDMI Splitter
- 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.
Avoid two common type and naming mistakes
- Use the primitive TypeScript type
stringfor string parameters, not the boxedStringtype; TypeScript’s Do’s and Don’ts guidance recommends the primitive type. - Do not confuse
text.lengthwithString.length. The latter refers to the arity of theStringfunction, not the length of a particular string. - Do not describe
.lengthas counting “characters” without specifying UTF-16 code units; combining marks and joined emoji can make the visible-character count different.
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