Function groupArrayElements

lib/internal/util/inspect.js:2045–2153

(ctx, output, value)

}

function groupArrayElements(ctx, output, value) {
  let totalLength = 0;
  let maxLength = 0;
  let i = 0;
  let outputLength = output.length;
  if (ctx.maxArrayLength < output.length) {
    // This makes sure the "... n more items" part is not taken into account.
    outputLength--;
  }
  const separatorSpace = 2; // Add 1 for the space and 1 for the separator.
  const dataLen = new Array(outputLength);
  // Calculate the total length of all output entries and the individual max
  // entries length of all output entries. We have to remove colors first,
  // otherwise the length would not be calculated properly.
  for (; i < outputLength; i++) {
    const len = getStringWidth(output[i], ctx.colors);
    dataLen[i] = len;
    totalLength += len + separatorSpace;
    if (maxLength < len)
      maxLength = len;
  }
  // Add two to `maxLength` as we add a single whitespace character plus a comma
  // in-between two entries.
  const actualMax = maxLength + separatorSpace;
  // Check if at least three entries fit next to each other and prevent grouping
  // of arrays that contains entries of very different length (i.e., if a single
  // entry is longer than 1/5 of all other entries combined). Otherwise the
  // space in-between small entries would be enormous.
  if (actualMax * 3 + ctx.indentationLvl < ctx.breakLength &&
      (totalLength / actualMax > 5 || maxLength <= 6)) {

    const approxCharHeights = 2.5;
    const averageBias = MathSqrt(actualMax - totalLength / output.length);
    const biasedMax = MathMax(actualMax - 3 - averageBias, 1);
    // Dynamically check how many columns seem possible.
    const columns = MathMin(
      // Ideally a square should be drawn. We expect a character to be about 2.5
      // times as high as wide. This is the area formula to calculate a square
      // which contains n rectangles of size `actualMax * approxCharHeights`.
      // Divide that by `actualMax` to receive the correct number of columns.
      // The added bias increases the columns for short entries.
      MathRound(
        MathSqrt(
          approxCharHeights * biasedMax * outputLength,
        ) / biasedMax,
      ),
      // Do not exceed the breakLength.
      MathFloor((ctx.breakLength - ctx.indentationLvl) / actualMax),
      // Limit array grouping for small `compact` modes as the user requested
      // minimal grouping.
      ctx.compact * 4,
      // Limit the columns to a maximum of fifteen.
      15,
    );
    // Return with the original output if no grouping should happen.
    if (columns <= 1) {
      return output;
    }