Overview of formatting numbers in JavaScript

JavaScript doesn't have many built-in methods to format numbers. Most of the time customized code needs to be used. Refer below for a couple rounding methods that JavaScript offers, then next up is some custom code I wrote to do more advanced formatting.

• Round to a certain number of places
  • Details
• Add commas
  • Details (Includes a function to format separators other than commas)
• Multi-functional number format script
  • Details
  • Interactive example
  • Syntax information

Round to a certain number of places

For rounding decimals you can use the built-in JavaScript methods toFixed or toPrecision.

var num = 10;
var result = num.toFixed(2); // result will equal 10.00

num = 930.9805;
result = num.toFixed(3); // result will equal 930.981

num = 500.2349;
result = num.toPrecision(4); // result will equal 500.2

num = 5000.2349;
result = num.toPrecision(4); // result will equal 5000

num = 555.55;
result = num.toPrecision(2); // result will equal 5.6e+2

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Add commas

This functionality is not built into JavaScript, so custom code needs to be used. The following is one way of adding commas to a number, and returning a string.

function addCommas(nStr)
{
	nStr += '';
	x = nStr.split('.');
	x1 = x[0];
	x2 = x.length > 1 ? '.' + x[1] : '';
	var rgx = /(\d+)(\d{3})/;
	while (rgx.test(x1)) {
		x1 = x1.replace(rgx, '$1' + ',' + '$2');
	}
	return x1 + x2;
}

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Multi-functional number format script

• commas (configurable digit grouping separators and decimal symbols)
• certain decimal precision that leave trailing zeros
• various formats for currency and negative values
• input can be a string that's already formatted

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Interactive example

Syntax information