Regular expressions remove spaces at both ends

Use regular substitution to remove the spaces before and after the string , Because some lower version browsers do not support trim() Method , So I made a judgment

<script type="javascript">
    let str = ' a i ldt ldt ';
    let newStr = function(str){
    
        if(str.trim){
       //  Some lower version browsers do not support this method , So judge first 
            return str.trim();
        }
        else{
       //  If the above method is not supported , Use regular 
            return str.replace(/^\s+|\s+$/g,"")
        }
    }
    console.log(newStr(str)); //a i ldt ldt
</script>

To remove the space in the middle , But write like this
trim() Method cannot remove the middle space

<script>
    let str = ' a i ldt ldt ';
    let newStr = function(str){
    
        return str.replace(/^\s+|\s+|\s+$/g,"")
    }
    console.log(newStr(str)); //aildtldt
</script>