Question

我想在语句中设置一些索引，并检查是否找到了此方法charAt，但它仅适用于字符串，因此如何使用数字处理它们

if (mobileNumber) {
        let j = mobileNumber.charAt(2);
        let w = mobileNumber.charAt(0);
        alert("@", w, j)
        if (j === 9) { //Not work quz it's a number
          alert("FoundJ", j)
          return;
        } else if (w === 6) { //Not work quz it's a number
          alert("FoundW", w)
          return
        } else{
           alert("sorry, App does not work in your city right now")
           return
          }

更新

现在我处理索引了，但是我对它们有一些疑问，这是我的声明如果我写这个数字并且它包含9 || （2）索引中的6我在调用不知道为什么的函数时看到警报？

 let j = mobileNumber.toString().charAt(2);
      if (mobileNumber.length <= 0) {
        this.setState(
          Object.assign(validations, {
            mobileNumberValid: "• Please, write your Mobile Number"
          })
        );
        return;
      } else if (mobileNumber.length < 10) {
        this.setState(
          Object.assign(validations, {
            mobileNumberValid:
              "• Your Mobile Number must be exactly 10 characters!"
          })
        );
        return;
      } else if (regNumber.test(mobileNumber) === false) {
        this.setState(
          Object.assign(validations, {
            mobileNumberValid: "• Please, Your mobile must be a number"
          })
        );
        return;
      }
      else if (j != 9 || j != 6) { // i think the issue with **OR** 
        alert("sorry not work in your city yet!")
        return;
      }
 else {
        this.setState(
          Object.assign(validations, {
            mobileNumberValid: ""
          })
        );
      }

Answer 1

首先使用toString()将数字转换为字符串，然后使用charAt(index)

var mobileNumber = 98812345;
console.log(mobileNumber.toString().charAt(1));

Answer 2

只需将它们转换为字符串即可：

if (mobileNumber) {
   let j = mobileNumber.toString().charAt(2);
   let w = mobileNumber.toString().charAt(0);
}

如果您需要将它们用作数字，只需将它们解析回去：

let jNumber = parseInt(j, 10);

Answer 3

===执行精确比较，而没有转换类型（据我所知）

如果您有数字表达式，可以将其转换为字符串，然后使用charAt（）进行比较

function findJW(mobileNumber) {
    console.log("Checking "+ mobileNumber)
    let str = mobileNumber.toString();
    let j = str.charAt(2);
    let w = str.charAt(0);
  
    if (j == '9') {
       console.log("FoundJ", j)
    } else if (w == '6') {
      console.log("FoundW", w)
    } else{
      console.log("sorry, App does not work in your city right now")
    }
}

findJW(12954678)
findJW(62354678)
findJW(11111111)

在Java中将charAt与数字一起使用

更新

3 个答案: