01_web_util.js

// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
"use strict";

((window) => {
  const illegalConstructorKey = Symbol("illegalConstructorKey");

  function requiredArguments(
    name,
    length,
    required,
  ) {
    if (length < required) {
      const errMsg = `${name} requires at least ${required} argument${
        required === 1 ? "" : "s"
      }, but only ${length} present`;
      throw new TypeError(errMsg);
    }
  }

  const objectCloneMemo = new WeakMap();

  function cloneArrayBuffer(
    srcBuffer,
    srcByteOffset,
    srcLength,
    _cloneConstructor,
  ) {
    // this function fudges the return type but SharedArrayBuffer is disabled for a while anyway
    return srcBuffer.slice(
      srcByteOffset,
      srcByteOffset + srcLength,
    );
  }

  /** Clone a value in a similar way to structured cloning.  It is similar to a
 * StructureDeserialize(StructuredSerialize(...)). */
  function cloneValue(value) {
    switch (typeof value) {
      case "number":
      case "string":
      case "boolean":
      case "undefined":
      case "bigint":
        return value;
      case "object": {
        if (objectCloneMemo.has(value)) {
          return objectCloneMemo.get(value);
        }
        if (value === null) {
          return value;
        }
        if (value instanceof Date) {
          return new Date(value.valueOf());
        }
        if (value instanceof RegExp) {
          return new RegExp(value);
        }
        if (value instanceof SharedArrayBuffer) {
          return value;
        }
        if (value instanceof ArrayBuffer) {
          const cloned = cloneArrayBuffer(
            value,
            0,
            value.byteLength,
            ArrayBuffer,
          );
          objectCloneMemo.set(value, cloned);
          return cloned;
        }
        if (ArrayBuffer.isView(value)) {
          const clonedBuffer = cloneValue(value.buffer);
          // Use DataViewConstructor type purely for type-checking, can be a
          // DataView or TypedArray.  They use the same constructor signature,
          // only DataView has a length in bytes and TypedArrays use a length in
          // terms of elements, so we adjust for that.
          let length;
          if (value instanceof DataView) {
            length = value.byteLength;
          } else {
            length = value.length;
          }
          return new (value.constructor)(
            clonedBuffer,
            value.byteOffset,
            length,
          );
        }
        if (value instanceof Map) {
          const clonedMap = new Map();
          objectCloneMemo.set(value, clonedMap);
          value.forEach((v, k) => {
            clonedMap.set(cloneValue(k), cloneValue(v));
          });
          return clonedMap;
        }
        if (value instanceof Set) {
          // assumes that cloneValue still takes only one argument
          const clonedSet = new Set([...value].map(cloneValue));
          objectCloneMemo.set(value, clonedSet);
          return clonedSet;
        }

        // default for objects
        const clonedObj = {};
        objectCloneMemo.set(value, clonedObj);
        const sourceKeys = Object.getOwnPropertyNames(value);
        for (const key of sourceKeys) {
          clonedObj[key] = cloneValue(value[key]);
        }
        Reflect.setPrototypeOf(clonedObj, Reflect.getPrototypeOf(value));
        return clonedObj;
      }
      case "symbol":
      case "function":
      default:
        throw new DOMException("Uncloneable value in stream", "DataCloneError");
    }
  }

  const handlerSymbol = Symbol("eventHandlers");
  function makeWrappedHandler(handler) {
    function wrappedHandler(...args) {
      if (typeof wrappedHandler.handler !== "function") {
        return;
      }
      return wrappedHandler.handler.call(this, ...args);
    }
    wrappedHandler.handler = handler;
    return wrappedHandler;
  }
  function defineEventHandler(emitter, name, defaultValue = undefined) {
    // HTML specification section 8.1.5.1
    Object.defineProperty(emitter, `on${name}`, {
      get() {
        return this[handlerSymbol]?.get(name)?.handler ?? defaultValue;
      },
      set(value) {
        if (!this[handlerSymbol]) {
          this[handlerSymbol] = new Map();
        }
        let handlerWrapper = this[handlerSymbol]?.get(name);
        if (handlerWrapper) {
          handlerWrapper.handler = value;
        } else {
          handlerWrapper = makeWrappedHandler(value);
          this.addEventListener(name, handlerWrapper);
        }
        this[handlerSymbol].set(name, handlerWrapper);
      },
      configurable: true,
      enumerable: true,
    });
  }
  window.__bootstrap.webUtil = {
    illegalConstructorKey,
    requiredArguments,
    defineEventHandler,
    cloneValue,
  };
})(this);