正常的写法是这样的

      if (newValue == 2) {
        this.is_abnormal = true;
      } else {
        if (this.form.motor != 2 && this.form.die != 2 && this.form.position != 2) {
          this.is_abnormal = false;
        }
      }

使用return和&&符号之后

      if (newValue == 2) {
        this.is_abnormal = true;
        return;// return后下面的代码不执行
      }
      // 判定&&前面为true时则执行&&后面的代码
      (this.form.motor != 2 && this.form.die != 2 && this.form.position != 2)
       && (this.is_abnormal = false);