src/source_map_support.js

function WasmSourceMap(sourceMap) {
  this.version = sourceMap.version;
  this.sources = sourceMap.sources;
  this.names = sourceMap.names;

  this.mapping = {};
  this.offsets = [];

  var vlqMap = {};
  'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/='.split('').forEach(function (c, i) {
    vlqMap[c] = i;
  });

  // based on https://github.com/Rich-Harris/vlq/blob/master/src/vlq.ts
  function decodeVLQ(string) {
    var result = [];
    var shift = 0;
    var value = 0;

    for (var i = 0; i < string.length; ++i) {
      var integer = vlqMap[string[i]];
      if (integer === undefined) {
        throw new Error('Invalid character (' + string[i] + ')');
      }

      value += (integer & 31) << shift;

      if (integer & 32) {
        shift += 5;
      } else {
        var negate = value & 1;
        value >>= 1;
        result.push(negate ? -value : value);
        value = shift = 0;
      }
    }
    return result;
  }

  var offset = 0, src = 0, line = 1, col = 1, name = 0;
  sourceMap.mappings.split(',').forEach(function (segment, index) {
    if (!segment) return;
    var data = decodeVLQ(segment);
    var info = {};

    offset += data[0];
    if (data.length >= 2) info.source = src += data[1];
    if (data.length >= 3) info.line = line += data[2];
    if (data.length >= 4) info.column = col += data[3];
    if (data.length >= 5) info.name = name += data[4];
    this.mapping[offset] = info;
    this.offsets.push(offset);
  }, this);
  this.offsets.sort(function (a, b) { return a - b; });
}

WasmSourceMap.prototype.lookup = function (offset) {
  var normalized = this.normalizeOffset(offset);
#if USE_OFFSET_CONVERTER
  if (!wasmOffsetConverter.isSameFunc(offset, normalized)) {
    return null;
  }
#endif
  var info = this.mapping[normalized];
  if (!info) {
    return null;
  }
  return {
    source: this.sources[info.source],
    line: info.line,
    column: info.column,
    name: this.names[info.name],
  };
}

WasmSourceMap.prototype.normalizeOffset = function (offset) {
  var lo = 0;
  var hi = this.offsets.length;
  var mid;

  while (lo < hi) {
    mid = Math.floor((lo + hi) / 2);
    if (this.offsets[mid] > offset) {
      hi = mid;
    } else {
      lo = mid + 1;
    }
  }
  return this.offsets[lo - 1];
}

var wasmSourceMapFile = '{{{ WASM_BINARY_FILE }}}.map';
if (!isDataURI(wasmBinaryFile)) {
  wasmSourceMapFile = locateFile(wasmSourceMapFile);
}

function getSourceMap() {
  try {
    return JSON.parse(read_(wasmSourceMapFile));
  } catch (err) {
    abort(err);
  }
}

function getSourceMapPromise() {
  if ((ENVIRONMENT_IS_WEB || ENVIRONMENT_IS_WORKER) && typeof fetch === 'function') {
    return fetch(wasmSourceMapFile, { credentials: 'same-origin' }).then(function(response) {
      return response['json']();
    }).catch(function () {
      return getSourceMap();
    });
  }
  return new Promise(function(resolve, reject) {
    resolve(getSourceMap());
  });
}