index.js

"use strict";

function makeException(ErrorType, message, opts = {}) {
    if (opts.globals) {
        ErrorType = opts.globals[ErrorType.name];
    }
    return new ErrorType(`${opts.context ? opts.context : "Value"} ${message}.`);
}

function toNumber(value, opts = {}) {
    if (!opts.globals) {
        return +value;
    }
    if (typeof value === "bigint") {
        throw opts.globals.TypeError("Cannot convert a BigInt value to a number");
    }
    return opts.globals.Number(value);
}

function type(V) {
    if (V === null) {
        return "Null";
    }
    switch (typeof V) {
        case "undefined":
            return "Undefined";
        case "boolean":
            return "Boolean";
        case "number":
            return "Number";
        case "string":
            return "String";
        case "symbol":
            return "Symbol";
        case "bigint":
            return "BigInt";
        case "object":
            // Falls through
        case "function":
            // Falls through
        default:
            // Per ES spec, typeof returns an implemention-defined value that is not any of the existing ones for
            // uncallable non-standard exotic objects. Yet Type() which the Web IDL spec depends on returns Object for
            // such cases. So treat the default case as an object.
            return "Object";
    }
}

// Round x to the nearest integer, choosing the even integer if it lies halfway between two.
function evenRound(x) {
    // There are four cases for numbers with fractional part being .5:
    //
    // case |     x     | floor(x) | round(x) | expected | x <> 0 | x % 1 | x & 1 |   example
    //   1  |  2n + 0.5 |  2n      |  2n + 1  |  2n      |   >    |  0.5  |   0   |  0.5 ->  0
    //   2  |  2n + 1.5 |  2n + 1  |  2n + 2  |  2n + 2  |   >    |  0.5  |   1   |  1.5 ->  2
    //   3  | -2n - 0.5 | -2n - 1  | -2n      | -2n      |   <    | -0.5  |   0   | -0.5 ->  0
    //   4  | -2n - 1.5 | -2n - 2  | -2n - 1  | -2n - 2  |   <    | -0.5  |   1   | -1.5 -> -2
    // (where n is a non-negative integer)
    //
    // Branch here for cases 1 and 4
    if ((x > 0 && (x % 1) === +0.5 && (x & 1) === 0) ||
        (x < 0 && (x % 1) === -0.5 && (x & 1) === 1)) {
        return censorNegativeZero(Math.floor(x));
    }

    return censorNegativeZero(Math.round(x));
}

function integerPart(n) {
    return censorNegativeZero(Math.trunc(n));
}

function sign(x) {
    return x < 0 ? -1 : 1;
}

function modulo(x, y) {
    // https://tc39.github.io/ecma262/#eqn-modulo
    // Note that http://stackoverflow.com/a/4467559/3191 does NOT work for large modulos
    const signMightNotMatch = x % y;
    if (sign(y) !== sign(signMightNotMatch)) {
        return signMightNotMatch + y;
    }
    return signMightNotMatch;
}

function censorNegativeZero(x) {
    return x === 0 ? 0 : x;
}

function createIntegerConversion(bitLength, typeOpts) {
    const isSigned = !typeOpts.unsigned;

    let lowerBound;
    let upperBound;
    if (bitLength === 64) {
        upperBound = Number.MAX_SAFE_INTEGER;
        lowerBound = !isSigned ? 0 : Number.MIN_SAFE_INTEGER;
    } else if (!isSigned) {
        lowerBound = 0;
        upperBound = Math.pow(2, bitLength) - 1;
    } else {
        lowerBound = -Math.pow(2, bitLength - 1);
        upperBound = Math.pow(2, bitLength - 1) - 1;
    }

    const twoToTheBitLength = Math.pow(2, bitLength);
    const twoToOneLessThanTheBitLength = Math.pow(2, bitLength - 1);

    return (V, opts = {}) => {
        let x = toNumber(V, opts);
        x = censorNegativeZero(x);

        if (opts.enforceRange) {
            if (!Number.isFinite(x)) {
                throw makeException(TypeError, "is not a finite number", opts);
            }

            x = integerPart(x);

            if (x < lowerBound || x > upperBound) {
                throw makeException(TypeError,
                    `is outside the accepted range of ${lowerBound} to ${upperBound}, inclusive`, opts);
            }

            return x;
        }

        if (!Number.isNaN(x) && opts.clamp) {
            x = Math.min(Math.max(x, lowerBound), upperBound);
            x = evenRound(x);
            return x;
        }

        if (!Number.isFinite(x) || x === 0) {
            return 0;
        }
        x = integerPart(x);

        // Math.pow(2, 64) is not accurately representable in JavaScript, so try to avoid these per-spec operations if
        // possible. Hopefully it's an optimization for the non-64-bitLength cases too.
        if (x >= lowerBound && x <= upperBound) {
            return x;
        }

        // These will not work great for bitLength of 64, but oh well. See the README for more details.
        x = modulo(x, twoToTheBitLength);
        if (isSigned && x >= twoToOneLessThanTheBitLength) {
            return x - twoToTheBitLength;
        }
        return x;
    };
}

function createLongLongConversion(bitLength, { unsigned }) {
    const upperBound = Number.MAX_SAFE_INTEGER;
    const lowerBound = unsigned ? 0 : Number.MIN_SAFE_INTEGER;
    const asBigIntN = unsigned ? BigInt.asUintN : BigInt.asIntN;

    return (V, opts = {}) => {
        let x = toNumber(V, opts);
        x = censorNegativeZero(x);

        if (opts.enforceRange) {
            if (!Number.isFinite(x)) {
                throw makeException(TypeError, "is not a finite number", opts);
            }

            x = integerPart(x);

            if (x < lowerBound || x > upperBound) {
                throw makeException(TypeError,
                    `is outside the accepted range of ${lowerBound} to ${upperBound}, inclusive`, opts);
            }

            return x;
        }

        if (!Number.isNaN(x) && opts.clamp) {
            x = Math.min(Math.max(x, lowerBound), upperBound);
            x = evenRound(x);
            return x;
        }

        if (!Number.isFinite(x) || x === 0) {
            return 0;
        }

        let xBigInt = BigInt(integerPart(x));
        xBigInt = asBigIntN(bitLength, xBigInt);
        return Number(xBigInt);
    };
}

exports.any = V => {
    return V;
};

exports.void = function () {
    return undefined;
};

exports.boolean = function (val) {
    return !!val;
};

exports.byte = createIntegerConversion(8, { unsigned: false });
exports.octet = createIntegerConversion(8, { unsigned: true });

exports.short = createIntegerConversion(16, { unsigned: false });
exports["unsigned short"] = createIntegerConversion(16, { unsigned: true });

exports.long = createIntegerConversion(32, { unsigned: false });
exports["unsigned long"] = createIntegerConversion(32, { unsigned: true });

exports["long long"] = createLongLongConversion(64, { unsigned: false });
exports["unsigned long long"] = createLongLongConversion(64, { unsigned: true });

exports.double = (V, opts) => {
    const x = toNumber(V, opts);

    if (!Number.isFinite(x)) {
        throw makeException(TypeError, "is not a finite floating-point value", opts);
    }

    return x;
};

exports["unrestricted double"] = (V, opts) => {
    const x = toNumber(V, opts);

    return x;
};

exports.float = (V, opts) => {
    const x = toNumber(V, opts);

    if (!Number.isFinite(x)) {
        throw makeException(TypeError, "is not a finite floating-point value", opts);
    }

    if (Object.is(x, -0)) {
        return x;
    }

    const y = Math.fround(x);

    if (!Number.isFinite(y)) {
        throw makeException(TypeError, "is outside the range of a single-precision floating-point value", opts);
    }

    return y;
};

exports["unrestricted float"] = (V, opts) => {
    const x = toNumber(V, opts);

    if (isNaN(x)) {
        return x;
    }

    if (Object.is(x, -0)) {
        return x;
    }

    return Math.fround(x);
};

exports.DOMString = function (V, opts = {}) {
    if (opts.treatNullAsEmptyString && V === null) {
        return "";
    }

    if (typeof V === "symbol") {
        throw makeException(TypeError, "is a symbol, which cannot be converted to a string", opts);
    }

    const StringCtor = opts.globals ? opts.globals.String : String;
    return StringCtor(V);
};

exports.ByteString = (V, opts) => {
    const x = exports.DOMString(V, opts);
    let c;
    for (let i = 0; (c = x.codePointAt(i)) !== undefined; ++i) {
        if (c > 255) {
            throw makeException(TypeError, "is not a valid ByteString", opts);
        }
    }

    return x;
};

exports.USVString = (V, opts) => {
    const S = exports.DOMString(V, opts);
    const n = S.length;
    const U = [];
    for (let i = 0; i < n; ++i) {
        const c = S.charCodeAt(i);
        if (c < 0xD800 || c > 0xDFFF) {
            U.push(String.fromCodePoint(c));
        } else if (0xDC00 <= c && c <= 0xDFFF) {
            U.push(String.fromCodePoint(0xFFFD));
        } else if (i === n - 1) {
            U.push(String.fromCodePoint(0xFFFD));
        } else {
            const d = S.charCodeAt(i + 1);
            if (0xDC00 <= d && d <= 0xDFFF) {
                const a = c & 0x3FF;
                const b = d & 0x3FF;
                U.push(String.fromCodePoint((2 << 15) + ((2 << 9) * a) + b));
                ++i;
            } else {
                U.push(String.fromCodePoint(0xFFFD));
            }
        }
    }

    return U.join("");
};

exports.object = (V, opts) => {
    if (type(V) !== "Object") {
        throw makeException(TypeError, "is not an object", opts);
    }

    return V;
};

// Not exported, but used in Function and VoidFunction.

// Neither Function nor VoidFunction is defined with [TreatNonObjectAsNull], so
// handling for that is omitted.
function convertCallbackFunction(V, opts) {
    if (typeof V !== "function") {
        throw makeException(TypeError, "is not a function", opts);
    }
    return V;
}

const abByteLengthGetter =
    Object.getOwnPropertyDescriptor(ArrayBuffer.prototype, "byteLength").get;
const sabByteLengthGetter =
    Object.getOwnPropertyDescriptor(SharedArrayBuffer.prototype, "byteLength").get;

function isNonSharedArrayBuffer(V) {
    try {
        // This will throw on SharedArrayBuffers, but not detached ArrayBuffers.
        // (The spec says it should throw, but the spec conflicts with implementations: https://github.com/tc39/ecma262/issues/678)
        abByteLengthGetter.call(V);

        return true;
    } catch {
        return false;
    }
}

function isSharedArrayBuffer(V) {
    try {
        sabByteLengthGetter.call(V);
        return true;
    } catch {
        return false;
    }
}

function isArrayBufferDetached(V) {
    try {
        // eslint-disable-next-line no-new
        new Uint8Array(V);
        return false;
    } catch {
        return true;
    }
}

exports.ArrayBuffer = (V, opts = {}) => {
    if (!isNonSharedArrayBuffer(V)) {
        if (opts.allowShared && !isSharedArrayBuffer(V)) {
            throw makeException(TypeError, "is not an ArrayBuffer or SharedArrayBuffer", opts);
        }
        throw makeException(TypeError, "is not an ArrayBuffer", opts);
    }
    if (isArrayBufferDetached(V)) {
        throw makeException(TypeError, "is a detached ArrayBuffer", opts);
    }

    return V;
};

const dvByteLengthGetter =
    Object.getOwnPropertyDescriptor(DataView.prototype, "byteLength").get;
exports.DataView = (V, opts = {}) => {
    try {
        dvByteLengthGetter.call(V);
    } catch (e) {
        throw makeException(TypeError, "is not a DataView", opts);
    }

    if (!opts.allowShared && isSharedArrayBuffer(V.buffer)) {
        throw makeException(TypeError, "is backed by a SharedArrayBuffer, which is not allowed", opts);
    }
    if (isArrayBufferDetached(V.buffer)) {
        throw makeException(TypeError, "is backed by a detached ArrayBuffer", opts);
    }

    return V;
};

// Returns the unforgeable `TypedArray` constructor name or `undefined`,
// if the `this` value isn't a valid `TypedArray` object.
//
// https://tc39.es/ecma262/#sec-get-%typedarray%.prototype-@@tostringtag
const typedArrayNameGetter = Object.getOwnPropertyDescriptor(
    Object.getPrototypeOf(Uint8Array).prototype,
    Symbol.toStringTag
).get;
[
    Int8Array, Int16Array, Int32Array, Uint8Array,
    Uint16Array, Uint32Array, Uint8ClampedArray, Float32Array, Float64Array
].forEach(func => {
    const name = func.name;
    const article = /^[AEIOU]/.test(name) ? "an" : "a";
    exports[name] = (V, opts = {}) => {
        if (!ArrayBuffer.isView(V) || typedArrayNameGetter.call(V) !== name) {
            throw makeException(TypeError, `is not ${article} ${name} object`, opts);
        }
        if (!opts.allowShared && isSharedArrayBuffer(V.buffer)) {
            throw makeException(TypeError, "is a view on a SharedArrayBuffer, which is not allowed", opts);
        }
        if (isArrayBufferDetached(V.buffer)) {
            throw makeException(TypeError, "is a view on a detached ArrayBuffer", opts);
        }

        return V;
    };
});

// Common definitions

exports.ArrayBufferView = (V, opts = {}) => {
    if (!ArrayBuffer.isView(V)) {
        throw makeException(TypeError, "is not a view on an ArrayBuffer or SharedArrayBuffer", opts);
    }

    if (!opts.allowShared && isSharedArrayBuffer(V.buffer)) {
        throw makeException(TypeError, "is a view on a SharedArrayBuffer, which is not allowed", opts);
    }

    if (isArrayBufferDetached(V.buffer)) {
        throw makeException(TypeError, "is a view on a detached ArrayBuffer", opts);
    }
    return V;
};

exports.BufferSource = (V, opts = {}) => {
    if (ArrayBuffer.isView(V)) {
        if (!opts.allowShared && isSharedArrayBuffer(V.buffer)) {
            throw makeException(TypeError, "is a view on a SharedArrayBuffer, which is not allowed", opts);
        }

        if (isArrayBufferDetached(V.buffer)) {
            throw makeException(TypeError, "is a view on a detached ArrayBuffer", opts);
        }
        return V;
    }

    if (!opts.allowShared && !isNonSharedArrayBuffer(V)) {
        throw makeException(TypeError, "is not an ArrayBuffer or a view on one", opts);
    }
    if (opts.allowShared && !isSharedArrayBuffer(V) && !isNonSharedArrayBuffer(V)) {
        throw makeException(TypeError, "is not an ArrayBuffer, SharedArrayBuffer, or a view on one", opts);
    }
    if (isArrayBufferDetached(V)) {
        throw makeException(TypeError, "is a detached ArrayBuffer", opts);
    }

    return V;
};

exports.DOMTimeStamp = exports["unsigned long long"];

exports.Function = convertCallbackFunction;

exports.VoidFunction = convertCallbackFunction;