如果JavaScript中的第一个字符不是数字，如何从字符串中删除呢？

Question

I have a text field on a form that allows individuals to enter a price. I'm trying to allow other currency symbols to be entered into this field but my logic behind the scenes needs to strip out any currency symbols.

To make it easier, I really only care about the first character and only if it's a non number.

Otherwise, I can't use a solution that would remove any decimal points or commas in my price field or my calculations won't work.

Update: I'm currently using itemCost = itemCost.replace(/\\$/, '');

But now I'm trying to open it up to any currency sign.

Answer 1

You can access a string in the same way as you would an array. Take a look at the character at position zero of the string -

var inputString = '...' // whatever the user entered
var firstChar = inputString[0];
if (!Number.isInteger(firstChar)) {
    inputString = inputString.substr(1)
}

I'm using the String.subStr function here to create a copy of the string starting from the 1st index.

Please take into consideration though that solution assumes that the provided string will only ever have one currency symbol. Inputs such as "USD $1.00" or even " $1.00" will not work with this solution.

---

An alternative would be to remove any character that is non numeric (excluding decimal points and commas) from the entire input string.

var inputString = '...' // whatever the user entered
var priceString = inputString.replace(/[^0-9\.,]/, '')

// $1.00 -> 1.00
// USD #$1,000.00 -> 1,000.00

Answer 2

Why don't you whitelist characters instead?

'$99,99'.match(/[0-9]+[,.]{0,1}[0-9]*/)

You'll certainly want to perfect it, I wrote it fast...

What the suggested regex does is make sure we have one or more digits, then maybe either a , or a . and 0 or more digits.

What I mostly want to point out with this answer is, while keeping just numeric characters is easy, it will by no mean make certain that the user entered a correct currency. The is also no way to know if the user entering 1,337 meant 1,337.00 or 1.337

Answer 3

You may use parseInt()

parseInt() parses a string and returns an integer.

If the first character cannot be converted to a number , parseInt() returns NaN .

parseInt('Hello') // returns NaN

Also it's a good idea to trim() the string before using parseInt()

 var money = '$123.45'; if( money ) { // check if variable is not null money = money.trim(); } console.log(parseInt(money)); // check NaN using isNaN function if(isNaN(parseInt(money))) { console.log('first charatcer is not a number') money = money.substr(1); console.log(money); } else { console.log('first charatcer is a number') } 

Answer 4

A Javscript function could be

// Function to check first letter as numbers

function chkNumeric(inputtxt)  
{

 var letterNumber = '^[0-9]{1,}[ a-zA-Z0-9]*$';  

 if((inputtxt.value.match(letterNumber))   
  {  

   return true;  

  }  

else  

  {   
   return false;   

  }  

  }

Answer 5

There's a few ways you can do this... One way is to make the input into an array, check isNaN on the first element, and strip it if it's not a number.

const input = '$123.45';
const otherInput = '23.34';


function splitCheck(someInput) {
  let arrayInput = someInput.split('');
  if (isNaN(arrayInput[0])) {
      arrayInput.shift();
      return arrayInput.join('');
  } else {
      return someInput;
  }
}

splitCheck(input); // returns 123.45
splitCheck(otherInput); // returns 23.34

Note you can also use a regexp, or you can also check for ASCII character values across an array, but this is just the first that came to mind.