The following code is written with JS tag. Let's test it. If 4 digits are not enough, add a space after it. For example, take 123 as an example:

var str = " 123 "；

if(str . length & lt； 4){

for(var I = 0； I < (4-string length); i++){

str+= " "；

}

}

if(str . length & gt； =4){

str = str.substring(0，4)；

}

document . write(str)；