How to use the source-map/base64-vlq.decode function in source-map

while (str.length > 0) {
        if (str.charAt(0) === ';') {
          generatedLine++;
          str = str.slice(1);
          previousGeneratedColumn = 0;
        }
        else if (str.charAt(0) === ',') {
          str = str.slice(1);
        }
        else {
          mapping = {};
          mapping.generatedLine = generatedLine;

          // Generated column.
          temp = base64VLQ.decode(str);
          mapping.generatedColumn = previousGeneratedColumn + temp.value;
          previousGeneratedColumn = mapping.generatedColumn;
          str = temp.rest;

          if (str.length > 0 && !mappingSeparator.test(str.charAt(0))) {
            // Original source.
            temp = base64VLQ.decode(str);
            if (aSourceRoot) {
              mapping.source = util.join(aSourceRoot, this._sources.at(previousSource + temp.value));
            }
            else {
              mapping.source = this._sources.at(previousSource + temp.value);
            }
            previousSource += temp.value;
            str = temp.rest;
            if (str.length === 0 || mappingSeparator.test(str.charAt(0))) {

// Lines are stored 0-based
            mapping.originalLine += 1;
            str = temp.rest;
            if (str.length === 0 || mappingSeparator.test(str.charAt(0))) {
              throw new Error('Found a source and line, but no column');
            }

            // Original column.
            temp = base64VLQ.decode(str);
            mapping.originalColumn = previousOriginalColumn + temp.value;
            previousOriginalColumn = mapping.originalColumn;
            str = temp.rest;

            if (str.length > 0 && !mappingSeparator.test(str.charAt(0))) {
              // Original name.
              temp = base64VLQ.decode(str);
              mapping.name = this._names.at(previousName + temp.value);
              previousName += temp.value;
              str = temp.rest;
            }
          }

          this._generatedMappings.push(mapping);
          this._originalMappings.push(mapping);
        }
      }

      this._originalMappings.sort(this._compareOriginalPositions);
    };