摘自http://ntt.cc/2008/04/25/6-very-basic-but-very-useful-javascript-number-format-functions-for-web-developers.html
重新发明轮子没有意义.. :)
/**
* Formats the number according to the ‘format’ string;
* adherses to the american number standard where a comma
* is inserted after every 3 digits.
* note: there should be only 1 contiguous number in the format,
* where a number consists of digits, period, and commas
* any other characters can be wrapped around this number, including ‘$’, ‘%’, or text
* examples (123456.789):
* ‘0′ - (123456) show only digits, no precision
* ‘0.00′ - (123456.78) show only digits, 2 precision
* ‘0.0000′ - (123456.7890) show only digits, 4 precision
* ‘0,000′ - (123,456) show comma and digits, no precision
* ‘0,000.00′ - (123,456.78) show comma and digits, 2 precision
* ‘0,0.00′ - (123,456.78) shortcut method, show comma and digits, 2 precision
*
* @method format
* @param format {string} the way you would like to format this text
* @return {string} the formatted number
* @public
*/
Number.prototype.format = function(format) {
if (! isType(format, ’string’)) {return ”;} // sanity check
var hasComma = -1 < format.indexOf(’,'),
psplit = format.stripNonNumeric().split(’.'),
that = this;
// compute precision
if (1 < psplit.length) {
// fix number precision
that = that.toFixed(psplit[1].length);
}
// error: too many periods
else if (2 < psplit.length) {
throw(’NumberFormatException: invalid format, formats should have no more than 1 period: ‘ + format);
}
// remove precision
else {
that = that.toFixed(0);
}
// get the string now that precision is correct
var fnum = that.toString();
// format has comma, then compute commas
if (hasComma) {
// remove precision for computation
psplit = fnum.split(’.');
var cnum = psplit[0],
parr = [],
j = cnum.length,
m = Math.floor(j / 3),
n = cnum.length % 3 || 3; // n cannot be ZERO or causes infinite loop
// break the number into chunks of 3 digits; first chunk may be less than 3
for (var i = 0; i < j; i += n) {
if (i != 0) {n = 3;}
parr[parr.length] = cnum.substr(i, n);
m -= 1;
}
// put chunks back together, separated by comma
fnum = parr.join(’,');
// add the precision back in
if (psplit[1]) {fnum += ‘.’ + psplit[1];}
}
// replace the number portion of the format with fnum
return format.replace(/[\d,?\.?]+/, fnum);
};