JavaScript内核系列 第5章 数组

var a＝[];
a[0] = 0;
a["1"] = 1;
a[new Number(2)] = 2;
a[new String(3)] = 3;
a[new Object(4)] = 4;

var MyObj = function(value){
	this.value = value;
	this.toString = function(){
		return this.value;
	}
}
a[new MyObj(5)] = 5;

    public static Object setObjectElem(Scriptable obj, Object elem,
                                       Object value, Context cx)
    {
        if (obj instanceof XMLObject) {
            XMLObject xmlObject = (XMLObject)obj;
            xmlObject.ecmaPut(cx, elem, value);
            return value;
        }

       [b] [color=red]String s = toStringIdOrIndex(cx, elem);[/color][/b]
        if (s == null) {
            int index = lastIndexResult(cx);
            ScriptableObject.putProperty(obj, index, value);                //属性elem可以作为index
        } else {
            ScriptableObject.putProperty(obj, s, value);                      //属性elem为其它
        }

        return value;
    }

    static String toStringIdOrIndex(Context cx, Object id)
    {
        if (id instanceof Number) {                           //如果属性为数字
            double d = ((Number)id).doubleValue();
            int index = (int)d;
            if (index == d) {
                storeIndexResult(cx, index);
                return null;
            }
            return toString(id);
        } else {
            String s;
            if (id instanceof String) {                          //如果属性为字符串
                s = (String)id;
            } else {
                s = toString(id);                                 //如果属性为其他，用toString方法得到其字符串值
            }
            long indexTest = indexFromString(s);       //这个方法判断这个字符串是否可以做index
            if (indexTest >= 0) {
                storeIndexResult(cx, (int)indexTest);
                return null;
            }
            return s;
        }
    }

    public static String toString(Object val) {
        for (;;) {
            if (val == null) {
                return "null";
            }
            if (val == Undefined.instance) {
                return "undefined";
            }
            if (val instanceof String) {
                return (String)val;
            }
            if (val instanceof Number) {
                // XXX should we just teach NativeNumber.stringValue()
                // about Numbers?
                return numberToString(((Number)val).doubleValue(), 10);
            }
            if (val instanceof Scriptable) {
                val = ((Scriptable) val).getDefaultValue(StringClass);
                if (val instanceof Scriptable) {
                    throw errorWithClassName("msg.primitive.expected", val);
                }
                continue;
            }
            return val.toString();         //如果只是一般的object，就是用其toString方法的返回值，
        }                                          //这个也就是我例子里所举的那个自定义对象的情况
    }

    public void put(int index, Scriptable start, Object value)
    {
        if (start == this && !isSealed() && dense != null && 0 <= index &&
            (denseOnly || !isGetterOrSetter(null, index, true)))
        {
            if (index < dense.length) {
                dense[index] = value;
                if (this.length <= index)
                    this.length = (long)index + 1;
                return;
            } else if (denseOnly && index < dense.length * GROW_FACTOR &&
                       ensureCapacity(index+1))
            {
                dense[index] = value;
                this.length = (long)index + 1;
                return;
            } else {
                denseOnly = false;
            }
        }
        super.put(index, start, value);             //这儿调用了super的方法，实际上上面的例子是没有走到这儿的。
        if (start == this) {
            // only set the array length if given an array index (ECMA 15.4.0)
            if (this.length <= index) {
                // avoid overflowing index!
                this.length = (long)index + 1;
            }
        }
    }