Method checkAssignmentOperator

internal/checker/checker.go:12719–12743

(left *ast.Node, operator ast.Kind, right *ast.Node, leftType *Type, rightType *Type)

}

func (c *Checker) checkAssignmentOperator(left *ast.Node, operator ast.Kind, right *ast.Node, leftType *Type, rightType *Type) {
	if ast.IsAssignmentOperator(operator) {
		// We ignore assignments of undefined to CommonJS exports when there are multiple assignment declarations
		if ast.IsDeclarationNode(left.Parent) && ast.GetAssignmentDeclarationKind(left.Parent) == ast.JSDeclarationKindExportsProperty {
			if symbol := c.symbolNodeLinks.Get(left).resolvedSymbol; symbol != nil && len(symbol.Declarations) > 1 && rightType.flags&TypeFlagsUndefined != 0 {
				return
			}
		}
		// getters can be a subtype of setters, so to check for assignability we use the setter's type instead
		if ast.IsCompoundAssignment(operator) && ast.IsPropertyAccessExpression(left) {
			leftType = c.checkPropertyAccessExpression(left, CheckModeNormal, true /*writeOnly*/)
		}
		if c.checkReferenceExpression(left, diagnostics.The_left_hand_side_of_an_assignment_expression_must_be_a_variable_or_a_property_access, diagnostics.The_left_hand_side_of_an_assignment_expression_may_not_be_an_optional_property_access) {
			var headMessage *diagnostics.Message
			if c.exactOptionalPropertyTypes && ast.IsPropertyAccessExpression(left) && c.maybeTypeOfKind(rightType, TypeFlagsUndefined) {
				target := c.getTypeOfPropertyOfType(c.getTypeOfExpression(left.Expression()), left.Name().Text())
				if c.isExactOptionalPropertyMismatch(rightType, target) {
					headMessage = diagnostics.Type_0_is_not_assignable_to_type_1_with_exactOptionalPropertyTypes_Colon_true_Consider_adding_undefined_to_the_type_of_the_target
				}
			}
			// to avoid cascading errors check assignability only if 'isReference' check succeeded and no errors were reported
			c.checkTypeAssignableToAndOptionallyElaborate(rightType, leftType, left, right, headMessage, nil)
		}
	}
}

func (c *Checker) bothAreBigIntLike(left *Type, right *Type) bool {
	return c.isTypeAssignableToKind(left, TypeFlagsBigIntLike) && c.isTypeAssignableToKind(right, TypeFlagsBigIntLike)