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javascript和执行步骤中的范围(scope in javascript and execution steps)

(function() {
            var a = 'g';
            function foo() {
                console.log(a);
                a = 7; //
            }
            console.log(foo(), a);
    }());

任何人都可以解释这个代码示例的逐步执行和输出。 我得到了'g undefined 7'


(function() {
            var a = 'g';
            function foo() {
                console.log(a);
                a = 7; //
            }
            console.log(foo(), a);
    }());

Can anybody explain the step by step execution and out put of this code sample. I got the out put as 'g undefined 7'


原文:https://stackoverflow.com/questions/32352419
更新时间:2021-09-05 10:09

最满意答案

这里有几件事情错了。

  1. 分隔符。 当您创建MySQL过程或触发器时,您需要非常明确地定义分隔符,以便查询解释器可以区分过程中行的末尾和声明的结尾。
  2. BEGIN声明的位置。 应该在FOR EACH ROW之后直接进行。
  3. 使用WHEN而不是IF。
  4. 使用PRINT代替SIGNAL SQLSTATE'...'SET MESSAGE_TEXT ='...'。 这就是你在MySQL 5.5+中引发异常的方法。

这是应该工作的代码!

DELIMITER $$

CREATE TRIGGER testa_trig  
BEFORE INSERT ON testa 
FOR EACH ROW BEGIN
    IF (NEW.c > 100) THEN 
        SIGNAL SQLSTATE '02000' SET MESSAGE_TEXT = 'Warning: c > 100!';
    END IF;
END$$

DELIMITER ;

Couple of things wrong here.

  1. Delimiters. When you make a MySQL procedure or trigger, you need to be very explicit about delimiters so the query interpreter can distinguish between ends of lines in your procedure and the end of your declaration.
  2. Location of the BEGIN statement. It should be directly after FOR EACH ROW.
  3. Use of WHEN instead of IF.
  4. Use of PRINT instead to SIGNAL SQLSTATE '...' SET MESSAGE_TEXT = '...'. This is how you raise exceptions in MySQL 5.5+.

Here is code that should work!

DELIMITER $$

CREATE TRIGGER testa_trig  
BEFORE INSERT ON testa 
FOR EACH ROW BEGIN
    IF (NEW.c > 100) THEN 
        SIGNAL SQLSTATE '02000' SET MESSAGE_TEXT = 'Warning: c > 100!';
    END IF;
END$$

DELIMITER ;

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