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Defne Eroğlu
Defne Eroğlu

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Truncate From Middle React Hook

I've published my very first npm package use-truncate-from-middle.
It is a react hook, dynamically truncates text from the middle with given ellipsis string (i.e. '...').
It considers the width of the container* and its font style.
In this blog, I am going to talk about the most common methods for truncating text and when you should use the useTruncateFromMiddle hook.
If you want to know the details about how the truncate from middle hook works, you can check my blog post
Calculate Number of Characters Fit into an HTML Element.

The Problem

In web development, if there is not enough space for a text, meaning the width of the container is a fixed value, we truncate it with ellipsis from the end. And it is very easy and safe to make this with pure CSS.
However, sometimes the width value of the container of the text is not set by the frontend team, meaning its value comes from an API call or an SDK or from a configuration file etc.
For such a case we have to include JavaScript along with CSS to truncate a long text dynamically.
In the next section, there are three most common methods to truncate long text with ellipsis from the end.

Traditional Ways To Truncate Text

Case 1: Single Line

I am pretty sure, especially if you are specialized in frontend development, you know by your heart the following css rules for truncating long text:

.truncate {
  width: 240px;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}
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Case 2: Multiple Line

If you need to truncate a text not at the first line, but in other lines, for example you have a container element which can hold maximum two lines of string, we use the following css rules:

.line-clamp {
  display: -webkit-box;
  -webkit-line-clamp: 2; // truncates at the second line
  -webkit-box-orient: vertical;  
  overflow: hidden;
}
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Case 3: Container Width Is Dynamic

In this case, we have to include Javascript along with CSS.
Especially thanks to CSS-IN-JS pattern it is very easy to make it. See below:

  const truncateStyle = {
    width: `${widthValue}`,
    whiteSpace: 'nowrap',
    overflow: 'hidden',
    textOverflow: 'ellipsis',
  };
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In the code block above, it just dynamically creates a style object with JavaScript.

Truncate Text From Middle

Static Method: Width of The Container Is Known

Function below truncates the text from the middle:

export const truncateFromMiddle = (
  fullStr= '',
  strLen,
  middleStr= '...',
) => {
  if (fullStr.length <= strLen) return fullStr;
  const midLen = middleStr.length;
  const charsToShow = strLen - midLen;
  const frontChars = Math.ceil(charsToShow / 2);
  const backChars = Math.floor(charsToShow / 2);
  return (
    fullStr.substr(0, frontChars) +
    middleStr+
    fullStr.substr(fullStr.length - backChars)
  );
};

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The function takes the original text that is fullStr and the parameter strLen that is the desired length should be shown in the UI.
As you see this method works, only if you know the width value of the container or say the frontend developer is the one who sets the width value in the .css file. The frontend developer decides when to truncate and how much to truncate. Therefore, if you know the width value and you need to truncate the text from the middle this kind of solution would be enough for you.

Width of The Container Is Not Set, It Depends On External Data

In this case we cannot set a static maximum strLen value, and truncate the text from middle using the previous truncateFromMiddle function. Because we cannot be sure about when to truncate, and when to show all text. And it is not just about the width actually, it varies depending on the font style as well. If font style value also comes externally, still we cannot be 100% sure when to truncate; for example a text with bold font and with large font size occupies more space than the small font size.
For these cases, you can use the useTruncateFromMiddle hook. It takes ref of the container element and its original text value as parameter.
Below you can see an example result of the hook:
example-for-the-hook-outcome

Conclusion

In this blog I tried to show the case where you need the useTruncateFromMiddle hook.
You can download and try the package if you have the opportunity or when you really need it. I plan to update the package in line with your feedback. Thank you for reading... Best.


*Container: i.e., div, span, button, read only textarea or any other non editable DOM elements.

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