What causes "Invalid argument passed to uncompress." in parallax/jsPDF?

Pass only the raw compressed string to uncompress().

parallax/jsPDF · error · Error

Invalid argument passed to uncompress.

Error message

Invalid argument passed to uncompress.

What it means

uncompress() is the inverse of the custom base16-like font-metrics encoding. It requires its input to be a string (the compressed payload); any non-string (object, number, null, undefined) throws 'Invalid argument passed to uncompress.' before parsing begins. This guards the parser from non-string input.

Source

Thrown at src/modules/standard_fonts_metrics.js:119

        }
      }
      vals.push(keystring + valuestring);
    }
    vals.push("}");
    return vals.join("");
  });

  /**
   * Uncompresses data compressed into custom, base16-like format.
   *
   * @public
   * @function
   * @param
   * @returns {Type}
   */
  var uncompress = (API.__fontmetrics__.uncompress = function(data) {
    if (typeof data !== "string") {
      throw new Error("Invalid argument passed to uncompress.");
    }

    var output = {},
      sign = 1,
      stringparts, // undef. will be [] in string mode
      activeobject = output,
      parentchain = [],
      parent_key_pair,
      keyparts = "",
      valueparts = "",
      key, // undef. will be Truthy when Key is resolved.
      datalen = data.length - 1, // stripping ending }
      ch;

    for (var i = 1; i < datalen; i += 1) {
      // - { } ' are special.

      ch = data[i];

View on GitHub (pinned to a3930ce03a)

Solutions

Pass only the raw compressed string to uncompress().
Guard: if (typeof data === 'string') API.__fontmetrics__.uncompress(data);
Avoid calling uncompress on data that is already a metrics object — check its type first.

Example fix

// before
const metrics = API.__fontmetrics__.uncompress(JSON.parse(raw)); // parse turned it into object -> throws [119]

// after
const metrics = API.__fontmetrics__.uncompress(typeof raw === 'string' ? raw : String(raw));

Defensive patterns

Strategy: type-guard

Validate before calling

function safeUncompress(data) {
  if (typeof data !== 'string') {
    throw new TypeError('uncompress expects a string payload');
  }
  return API.__fontmetrics__.uncompress(data);
}

Type guard

function isCompressedString(data) { return typeof data === 'string'; }

Try / catch

try {
  metrics = API.__fontmetrics__.uncompress(payload);
} catch (e) {
  if (/Invalid argument passed to uncompress/.test(e.message)) {
    // payload was already an object — use it directly instead of uncompressing
    metrics = payload;
  } else throw e;
}

Prevention

Pass only the raw compressed string; do not JSON.parse it first.
Do not double-process metrics that are already decompressed.
Guard with a typeof check before calling uncompress.

When it happens

Trigger: Calling API.__fontmetrics__.uncompress() with an object, number, null, or undefined; passing already-decompressed metric data back in; loading metrics from a source that returned a parsed object instead of the raw string.

Common situations: Double-decompressing (feeding an object that was already uncompressed); JSON.parse-ing the payload before uncompress; null returned from a failed fetch passed straight through.

Related errors

AI-assisted analysis of parallax/jsPDF@a3930ce03a (2026-08-13). Data as JSON: /api/errors/f46104d5a1ca8f1b. Report an issue: GitHub.