Function convertToInt

lib/internal/webidl.js:321–516

* Converts a JavaScript value to a Web IDL integer value. * @see https://webidl.spec.whatwg.org/#abstract-opdef-converttoint * @param {any} V JavaScript value. * @param {number} bitLength Integer bit length. * @param {'signed'|'unsigned'} [signedness] Integer signedness. * @param {ConversionOpt

(
  V,
  bitLength,
  signedness = 'unsigned',
  options = kEmptyObject,
)

 * @returns {number}
 */
function convertToInt(
  V,
  bitLength,
  signedness = 'unsigned',
  options = kEmptyObject,
) {
  const signed = signedness === 'signed';
  let upperBound;
  let lowerBound;

  // Web IDL ConvertToInt steps 1-3: determine lower/upper bounds.
  if (bitLength === 64) {
    // Steps 1.1-1.3 set upperBound to 2^53 - 1 and lowerBound to 0
    // for unsigned, or -2^53 + 1 for signed. This ensures 64-bit
    // integer types associated with [EnforceRange] or [Clamp] are
    // representable in JavaScript's Number type as unambiguous integers.
    upperBound = NumberMAX_SAFE_INTEGER;
    lowerBound = signed ? NumberMIN_SAFE_INTEGER : 0;
  } else if (!signed) {
    // Spell out the common Web IDL integer sizes so hot converters avoid
    // recomputing powers of two on every call.
    lowerBound = 0;
    if (bitLength === 8) {
      upperBound = 0xff;
    } else if (bitLength === 16) {
      upperBound = 0xffff;
    } else if (bitLength === 32) {
      upperBound = 0xffff_ffff;
    } else {
      upperBound = pow2(bitLength) - 1;
    }
  } else if (bitLength === 8) {
    // Signed 8/16/32-bit conversions are mostly exercised through direct
    // convertToInt() calls, but keep their common bounds cheap too.
    lowerBound = -0x80;
    upperBound = 0x7f;
  } else if (bitLength === 16) {
    lowerBound = -0x8000;
    upperBound = 0x7fff;
  } else if (bitLength === 32) {
    lowerBound = -0x8000_0000;
    upperBound = 0x7fff_ffff;
  } else {
    lowerBound = -pow2(bitLength - 1);
    upperBound = pow2(bitLength - 1) - 1;
  }

  // Common case: primitive Number values that already fit the Web IDL
  // range and have no fractional part are returned unchanged by every
  // ConvertToInt path, except that -0 must become +0. This skips the
  // generic ToNumber and option handling without skipping observable
  // object coercion.
  let x;
  if (typeof V === 'number') {
    // For primitive Numbers, in-range non-[Clamp] conversion is either
    // identity or IntegerPart(V). This keeps the default and [EnforceRange]
    // paths out of the generic ToNumber/options flow.
    if (V >= lowerBound && V <= upperBound) {