@awayfl/avm2/lib/run/HasNext2Info.ts

Virtual machine for executing AS3 code

import { safeGetPrototypeOf } from './safeGetPrototypeOf';
import { isNullOrUndefined } from '@awayfl/swf-loader';
import { AXObject } from './AXObject';

export class HasNext2Info {
	constructor(public object: AXObject, public index: number) {
		// ...
	}

	/**
     * Determine if the given object has any more properties after the specified |index| and if so,
     * return the next index or |zero| otherwise. If the |obj| has no more properties then continue
     * the search in
     * |obj.__proto__|. This function returns an updated index and object to be used during
     * iteration.
     *
     * the |for (x in obj) { ... }| statement is compiled into the following pseudo bytecode:
     *
     * index = 0;
     * while (true) {
     *   (obj, index) = hasNext2(obj, index);
     *   if (index) { #1
     *     x = nextName(obj, index); #2
     *   } else {
     *     break;
     *   }
     * }
     *
     * #1 If we return zero, the iteration stops.
     * #2 The spec says we need to get the nextName at index + 1, but it's actually index - 1, this
     * caused me two hours of my life that I will probably never get back.
     *
     * TODO: We can't match the iteration order semantics of Action Script, hopefully programmers
     * don't rely on it.
     */
	next(object: AXObject, index: number) {
		if (isNullOrUndefined(object)) {
			this.index = 0;
			this.object = null;
			return;
		} else {
			this.object = object;
			this.index = index;
		}
		let nextIndex = object.axNextNameIndex(this.index);
		if (nextIndex > 0) {
			this.index = nextIndex;
			return;
		}
		// If there are no more properties in the object then follow the prototype chain.
		while (!(nextIndex > 0)) {
			object = safeGetPrototypeOf(object);
			if (!object) {
				this.index = 0;
				this.object = null;
				return;
			}
			nextIndex = object.axNextNameIndex(0);
		}

		this.index = nextIndex;
		this.object = object;
		return;
	}
}