Truncate string at whitespace

JavaScript, String · Oct 21, 2020

Truncates a string up to specified length, respecting whitespace when possible.

Determine if String.prototype.length is greater or equal to lim. If not, return it as-is.
Use String.prototype.slice() and String.prototype.lastIndexOf() to find the index of the last space below the desired lim.
Use String.prototype.slice() to appropriately truncate str based on lastSpace, respecting whitespace if possible and appending ending at the end.
Omit the third argument, ending, to use the default ending of '...'.

const truncateStringAtWhitespace = (str, lim, ending = '...') => {
  if (str.length <= lim) return str;
  const lastSpace = str.slice(0, lim - ending.length + 1).lastIndexOf(' ');
  return str.slice(0, lastSpace > 0 ? lastSpace : lim - ending.length) + ending;
};

truncateStringAtWhitespace('short', 10); // 'short'
truncateStringAtWhitespace('not so short', 10); // 'not so...'
truncateStringAtWhitespace('trying a thing', 10); // 'trying...'
truncateStringAtWhitespace('javascripting', 10); // 'javascr...'

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