demo/typescript.js
function getTypeForBindingElement(declaration) {
            var pattern = declaration.parent;
            var parentType = getTypeForBindingElementParent(pattern.parent);
            // If parent has the unknown (error) type, then so does this binding element
            if (parentType === unknownType) {
                return unknownType;
            }
            // If no type was specified or inferred for parent, or if the specified or inferred type is any,
            // infer from the initializer of the binding element if one is present. Otherwise, go with the
            // undefined or any type of the parent.
            if (!parentType || isTypeAny(parentType)) {
                if (declaration.initializer) {
                    return checkExpressionCached(declaration.initializer);
                }
                return parentType;
            }
            var type;
            if (pattern.kind === 161 /* ObjectBindingPattern */) {
                // Use explicitly specified property name ({ p: xxx } form), or otherwise the implied name ({ p } form)
                var name_10 = declaration.propertyName || declaration.name;
                // Use type of the specified property, or otherwise, for a numeric name, the type of the numeric index signature,
                // or otherwise the type of the string index signature.
                type = getTypeOfPropertyOfType(parentType, name_10.text) ||
                    isNumericLiteralName(name_10.text) && getIndexTypeOfType(parentType, 1 /* Number */) ||
                    getIndexTypeOfType(parentType, 0 /* String */);
                if (!type) {
                    error(name_10, ts.Diagnostics.Type_0_has_no_property_1_and_no_string_index_signature, typeToString(parentType), ts.declarationNameToString(name_10));
                    return unknownType;
                }
            }
            else {
                // This elementType will be used if the specific property corresponding to this index is not
                // present (aka the tuple element property). This call also checks that the parentType is in
                // fact an iterable or array (depending on target language).
                var elementType = checkIteratedTypeOrElementType(parentType, pattern, /*allowStringInput*/ false);
                if (!declaration.dotDotDotToken) {
                    // Use specific property type when parent is a tuple or numeric index type when parent is an array
                    var propName = "" + ts.indexOf(pattern.elements, declaration);
                    type = isTupleLikeType(parentType)
                        ? getTypeOfPropertyOfType(parentType, propName)
                        : elementType;
                    if (!type) {
                        if (isTupleType(parentType)) {
                            error(declaration, ts.Diagnostics.Tuple_type_0_with_length_1_cannot_be_assigned_to_tuple_with_length_2, typeToString(parentType), parentType.elementTypes.length, pattern.elements.length);
                        }
                        else {
                            error(declaration, ts.Diagnostics.Type_0_has_no_property_1, typeToString(parentType), propName);
                        }
                        return unknownType;
                    }
                }
                else {
                    // Rest element has an array type with the same element type as the parent type
                    type = createArrayType(elementType);
                }
            }
            return type;
        }
function getTypeForBindingElement(declaration) {
            var pattern = declaration.parent;
            var parentType = getTypeForBindingElementParent(pattern.parent);
            // If parent has the unknown (error) type, then so does this binding element
            if (parentType === unknownType) {
                return unknownType;
            }
            // If no type was specified or inferred for parent, or if the specified or inferred type is any,
            // infer from the initializer of the binding element if one is present. Otherwise, go with the
            // undefined or any type of the parent.
            if (!parentType || isTypeAny(parentType)) {
                if (declaration.initializer) {
                    return checkExpressionCached(declaration.initializer);
                }
                return parentType;
            }
            var type;
            if (pattern.kind === 161 /* ObjectBindingPattern */) {
                // Use explicitly specified property name ({ p: xxx } form), or otherwise the implied name ({ p } form)
                var name_10 = declaration.propertyName || declaration.name;
                // Use type of the specified property, or otherwise, for a numeric name, the type of the numeric index signature,
                // or otherwise the type of the string index signature.
                type = getTypeOfPropertyOfType(parentType, name_10.text) ||
                    isNumericLiteralName(name_10.text) && getIndexTypeOfType(parentType, 1 /* Number */) ||
                    getIndexTypeOfType(parentType, 0 /* String */);
                if (!type) {
                    error(name_10, ts.Diagnostics.Type_0_has_no_property_1_and_no_string_index_signature, typeToString(parentType), ts.declarationNameToString(name_10));
                    return unknownType;
                }
            }
            else {
                // This elementType will be used if the specific property corresponding to this index is not
                // present (aka the tuple element property). This call also checks that the parentType is in
                // fact an iterable or array (depending on target language).
                var elementType = checkIteratedTypeOrElementType(parentType, pattern, /*allowStringInput*/ false);
                if (!declaration.dotDotDotToken) {
                    // Use specific property type when parent is a tuple or numeric index type when parent is an array
                    var propName = "" + ts.indexOf(pattern.elements, declaration);
                    type = isTupleLikeType(parentType)
                        ? getTypeOfPropertyOfType(parentType, propName)
                        : elementType;
                    if (!type) {
                        if (isTupleType(parentType)) {
                            error(declaration, ts.Diagnostics.Tuple_type_0_with_length_1_cannot_be_assigned_to_tuple_with_length_2, typeToString(parentType), parentType.elementTypes.length, pattern.elements.length);
                        }
                        else {
                            error(declaration, ts.Diagnostics.Type_0_has_no_property_1, typeToString(parentType), propName);
                        }
                        return unknownType;
                    }
                }
                else {
                    // Rest element has an array type with the same element type as the parent type
                    type = createArrayType(elementType);
                }
            }
            return type;
        }
Return the inferred type for a binding element