ellipsisify.js

/**
 * ellipsisify
 * @param {string} filename - The filename to be truncated.
 * @param {number} lengthThreshold - (optional) The minimum length of filename to truncate.
 */

export const ellipsisify = (filename, lengthThreshold = 20) => {
    // just return the filename if it's less than 20 characters long
    if (filename.length < lengthThreshold) return filename;


    // calculate a reasonable value for `sideLength` which will represent
    // the number of characters on either side of the … (&hellip;) character
    // (not including the final dot and extension name)
    const sideLength = Math.floor(lengthThreshold / 2.5);
    
    // break the filename into 2 (or more) pieces, creating a new array
    // i.e. [‘whoa-this-is-a-crazy-long-filename’, ‘png’]
    const filenamePieces = filename.split('.');
    
    // capture the last element of the array (the extension) into a variable
    const extension = filenamePieces.pop();
    
    // with `filenameBeforeExtension` we’re making sure that we take all the pieces of the array except
    // the last piece, and gluing them back together if necessary. In our example it doesn’t matter,
    // but if the filename were something like `whoa.this.is.a.crazy.long.filename.png`
    // then we would have gotten an array like this in the previous step
    // [‘whoa’, ‘this’, ‘is’, ‘a’, ‘crazy’, ‘long’, ‘filename’, ‘png’], therefore
    // we’d have to join all of those pieces back together and restore the dots as well
    const filenameBeforeExtension = filenamePieces.slice(0, filenamePieces.length).join('.');
    
    // now that we’ve got our final filename string (without the extension) we want the first number
    // of letters (the value of `sideLength`) and the last letters to be captured in their own variables
    const firstLetters = filenameBeforeExtension.substring(0, sideLength);
    const lastLetters = filenameBeforeExtension.substring(filenameBeforeExtension.length - sideLength);


    // finally, glue it all back together and return the final string!
    return `${firstLetters}…${lastLetters}.${extension}`;
};