js判断不能为数字

isNaN('Hello'); // true，因为'Hello'转换为数字是NaN
isNaN('123');   // false，因为'123'转换为数字是123
isNaN({});      // true，因为对象转换为数字是NaN

Number.isNaN('Hello'); // false，因为'Hello'不是一个NaN值
Number.isNaN(NaN);     // true，因为传入的值就是NaN
Number.isNaN({});      // false，因为{}不是一个NaN值

function checkNotNumber(value) {
  if (Number.isNaN(value)) {
    console.log('The value is NaN and cannot be a number.');
  } else {
    console.log('The value is a number or can be converted to a number.');
  }
}

checkNotNumber(NaN);       // The value is NaN and cannot be a number.
checkNotNumber('123');     // The value is a number or can be converted to a number.
checkNotNumber('Hello');   // The value is a number or can be converted to a number.
checkNotNumber(undefined); // The value is a number or can be converted to a number. (因为undefined转换为数字是NaN，但是Number.isNaN(undefined)返回false)

function checkCannotBeNumber(value) {
  if (isNaN(value) && Number.isNaN(Number(value))) {
    console.log('The value cannot be converted to a number.');
  } else {
    console.log('The value is a number or can be converted to a number.');
  }
}

checkCannotBeNumber(undefined); // The value cannot be converted to a number.