Huawei machine test question: String transformation minimum string JS

Title Description ：
Given a string s, You can only transform once at most , Returns the smallest string that can be obtained after transformation （ Compare in dictionary order ）.
Changing rules ： Swap characters at any two different positions in the string .
Input description ：
A string of lowercase letters s.
Output description ：
The minimum string obtained by transforming as required .
remarks ：
s Are all lowercase characters
1<=s.length<=1000
Example
Input ：abcdef

Output ：abcdef

explain ：abcdef Is already the smallest string , No exchange required

Input ：bcdefa

Output ：acdefb

explain ：a and b Exchange positions , Can get the minimum string

  let a=readline()
	   let res=a,b=a.split('').sort()
		  for(let i=0;i<a.length;i++){
			  if(a[i]!=b[i]){
				  let p=a.lastIndexOf(b[i])
				  res=a.slice(0,i)+b[i]+a.slice(i+1,p)+a[i]+a.slice(p+1)
				  break
			  }
		  }
	 
		console.log(res)

the second

 let a=readline()
	   let res=a.split('')
		  for(let i=0;i<a.length;i++){
			let p=a[i],t=i
			for(let j=i+1;j<a.length;j++){
				if(a[j]<p){
                  	p=a[j]
					t=j
				}
			}
			if(t!=i){
				res[i]=p
				res[t]=a[i]
				break
			}
		  }
	 
		console.log(res.join(''))