根据输入设计自定义文件编号字符串

Question

I really need your help with this since this goes well beyond my level of capability of javascript coding.

I'd like to design a function that would accomplish one of the following two scenarios:

1. If there is no dash and number at the end of the string var 'fileno', then rewrite the string fileno and add the dash and then the count at the end.

   var fileno = 'test'

   var c = 4

   fileno = 'test-4'

2. If there is already a dash and then a number at the end of the string, replace the dash-number with the new info below:

   var fileno = 'test-2'

   var c = 3

   fileno = 'test-3'

Answer 1

You may use regular expression with String.prototype.replace() :

fileno = fileno.replace(/-\d+$|$/, '-' + c);

It literally means: replace -{number} or nothing at the end of the string with -{c} .

 var c = 3; console.log( 'test'.replace(/-\\d+$|$/, '-' + c) ); console.log( 'test-4'.replace(/-\\d+$|$/, '-' + c) ); 

Answer 2

if(fileno[fileno.length - 2] === "-"){
  fileno = fileno.substr(0,-1) + c;
} else {
  fileno += "-" + c;
}

Just either append a new number if there is already a - in the second last position or append a new one.