Question

此代码使用现有数组将该数据填充为空数据......

然后它创建一个循环，检查它们是否低于18或大于等于18。

将数据填入空数组
检查不起作用

＆＃13;

var years = [1990, 2001, 1975, 2004, 1998, 1993];
var empty = [];
for (i = 0; i <= years.length - 1; i++) {
  empty.push(years[i]);
}
console.log(empty);
for (a = 0; a <= empty.length - 1; a++) {
  if (2018 - empty[a] < 18) {
    console.log(empty[a] + ' is not eighteen or older: ' + 2018 - empty[a]);
  } else {
    console.log(empty[a] + ' is eighteen or older: ' + 2018 - empty[a]);
  }
}

＆＃13;

Answer 1

它与字符串连接有关。由于2018是一个预期在这些控制台日志中进行数字加法的数字。我使用模板文字修改了你的代码，它工作正常。如果您不想使用模板文字，只需在最后2018 - empty[a]的计算周围添加括号变为(2018 - empty[a])。

＆＃13;

var years = [1990, 2001, 1975, 2004, 1998, 1993];
var empty = [];
for (let i = 0; i < years.length; i += 1) {
  empty.push(years[i]);
}
console.log(empty);
// using template literals
for (let a = 0; a < empty.length; a += 1) {
  if (2018 - +empty[a] < 18) {
    console.log(`${empty[a]} is not eighteen or older: ${2018 - empty[a]}`);
  } else {
    console.log(`${empty[a]} is eighteen or older: ${2018 - empty[a]}`);
  }
}

// regular string concatenation
for (let a = 0; a < empty.length; a += 1) {
  if (2018 - +empty[a] < 18) {
    console.log(empty[a] + ' is not eighteen or older:' + (2018 - empty[a]));
  } else {
    console.log(empty[a] + ' is eighteen or older:' + (2018 - empty[a]));
  }
}

＆＃13;

Answer 2

您看到的错误与运算符，类型强制和评估顺序有关。

您的console.log等同于下面显示的第一个+。你从一个数字开始，然后添加+ 2018一个字符串，所以整个事情被强制转换成一个字符串这将继续，所有内容都包含-字符串，直到您点击减号+ 2018 - empty[a]运算符为止 "2003 is not eighteen or older: 2018"

此时，减号不对字符串进行操作，并且到那里的值有一个字符串，例如：
NaN
所以尝试从字符串中减去一个数字会得到非数字"2003 is not eighteen or older: 2018" - empty[a]
console.log ( 5 + ' is five, subtract ' + 2 + ' is ' + 5-2 ); NaN

console.log ( 5 + ' is five, subtract ' + 2 + ' is ' + (5-2) );
5 is five, subtract 2 is 3

如果您对数字表达式进行括号，以便在与字符串连接之前对进行求值，则它应该有效：

console.log( empty[a] + ' is not eighteen or older: ' + (2018 - empty[a]) );

e.g。 var years = [1990, 2001, 1975, 2004, 1998, 1993]; var empty = []; for (i = 0; i <= years.length - 1; i++) { empty.push(years[i]); } console.log(empty); for (a = 0; a <= empty.length - 1; a++) { if (2018 - empty[a] < 18) { console.log( empty[a] + ' is not eighteen or older: ' + (2018 - empty[a]) ); } else { console.log( empty[a] + ' is eighteen or older: ' + (2018 - empty[a]) ); } }

2018 - empty[a]

注意 - 如果您计算一次年龄，然后在console.log输出中使用它，这也不会有问题。实际上，您多次计算for (a = 0; a <= empty.length - 1; a++) { let age = 2018 - empty[a]; if (age < 18) { console.log(empty[a] + ' is not eighteen or older: ' + age); ...。

var years = [1990, 2001, 1975, 2004, 1998, 1993]; var empty = []; for (i = 0; i <= years.length - 1; i++) { empty.push(years[i]); } console.log(empty); for (a = 0; a <= empty.length - 1; a++) { let age = 2018 - empty[a]; if (age < 18) { console.log( empty[a] + ' is not eighteen or older: ' + age ); } else { console.log( empty[a] + ' is eighteen or older: ' + age ); } }

getDoc() { return this.getError() .retryWhen((errors: any) => { return errors.switchMap((sourceError) => { console.log(sourceError); if (sourceError.status === 103) { console.log('status is 103'); const notFoundError = new HttpErrorResponse({ status: 404 }); return errors.delay(5000).take(5).concat(Observable.throw(notFoundError)); } return Observable.throw(sourceError); }); }) .toPromise(); } getError() { console.log('getting error'); return Observable.throw(new HttpErrorResponse({ status: 103 })); }

我的javascript代码中的错误是什么？我无法找到错误

2 个答案: