Function? Formatnumber (value, num){

var？ First,? b，？ c，？ Me;

Answer? =? value . tostring()；

b？ =? a.indexOf(" . ");

c？ =? A. length;

What if? (num？ ==? 0)? {

What if? (b？ ! =? - 1)? {

Answer? =? a.substring(0，b)；

}

}? Or what? {//If there is no decimal point,

What if? (b？ ==? - 1)? {

Answer? =? Answer? +? "."；

For what? (me? =? 1; ? Me? & lt=? num？ i++)？ {

Answer? =? Answer? +? "0";

}

}? Or what? {//There is a decimal point; if it exceeds the digits, it will be automatically intercepted; Otherwise, 0 will be added.

Answer? =? a.substring(0，b？ +? num？ +? 1);

For what? (me? =? c； ? Me? & lt=? b？ +? num？ i++)？ {

Answer? =? Answer? +? "0";

}

}

}

Return? a；

}

alert(formatnumber(3. 1，4))； //How to use it. The first parameter is the decimal number to be converted, and the second is the number of digits.