数値を日本語桁区切り文字列で返す

/**
 * 数値を日本語に変換
 *
 * @param mixed num 数値
 * @param string 前に付ける
 * @param string 後ろに付ける
 * @return string 変換後の文字列
 */
var jpNum = function(num, before, after) {
	String.prototype.lastFourNum = function() {
		return this.substr(strNum.length - 4).replace(/^0+/,'');
	}
	String.prototype.withoutLastFour = function() {
		return this.substr(0,this.length - 4);
	}
	if (typeof before === 'undefined') {
		before = '';
	}
	if (typeof after === 'undefined') {
		after = '';
	}
	var strNum = String(num);
	if (strNum == '') {
		return '';
	}
	var minusFlag = false;
	if (strNum.substr(0,1) == '-') {
		minusFlag = true;
		strNum = strNum.substr(1);
	}
	var ichi = '';
	if (strNum.length > 4) {
		ich = strNum.lastFourNum();
		strNum = strNum.withoutLastFour();
	} else {
		ich = strNum;
		strNum = '';
	}
	var man = '';
	if (strNum.length > 4) {
		man = strNum.lastFourNum();
		strNum = strNum.withoutLastFour();
	} else {
		man = strNum;
		strNum = '';
	}
	var oku = '';
	if (strNum.length > 4) {
		oku = strNum.lastFourNum();
		strNum = strNum.withoutLastFour();
	} else {
		oku = strNum;
		strNum = '';
	}
	var cho = '';
	if (strNum.length > 4) {
		cyo = strNum.lastFourNum();
		strNum = strNum.withoutLastFour();
	} else {
		cyo = strNum;
		strNum = '';
	}
	var result = '';
	if (cyo != '') {
		result += cyo + '兆';
	}
	if (oku != '') {
		result += oku + '億';
	}
	if (man != '') {
		result += man + '万';
	}
	if (ich != '') {
		result += ich;
	}
	if (minusFlag) {
		return before + '-' + result + after;
	} else {
		return before + result + after;
	}
}