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extended POSIX-style sprintf

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30.6 kB

Package description

What is extsprintf?

The extsprintf npm package provides extended sprintf-style formatting capabilities. It is designed to offer more powerful and flexible string formatting options than the traditional sprintf function found in many programming languages. This package allows for formatting strings with placeholders, enabling the insertion of variable content in a template-like fashion. It supports various formatting types, including numbers, strings, and JSON objects, making it suitable for a wide range of applications such as logging, message formatting, and text processing.

What are extsprintf's main functionalities?

Basic String Formatting

This feature allows for basic string formatting using placeholders for strings (%s) and decimal integers (%d). It is useful for constructing messages with dynamic values.

"%s is %d years old.", 'John', 25

Conditional Formatting

Conditional formatting supports inserting values from an object into a string based on property names. This is particularly useful for templating and creating more readable code.

"%(name)s is %(age)d years old.", { name: 'John', age: 25 }

JSON Formatting

This feature allows for the formatting of objects as JSON strings using the %j placeholder. It's useful for logging or displaying structured data in a string format.

"%j", { name: 'John', age: 25 }

Other packages similar to extsprintf



extsprintf: extended POSIX-style sprintf

Stripped down version of s[n]printf(3c). We make a best effort to throw an exception when given a format string we don't understand, rather than ignoring it, so that we won't break existing programs if/when we go implement the rest of this.

This implementation currently supports specifying

  • field alignment ('-' flag),
  • zero-pad ('0' flag)
  • always show numeric sign ('+' flag),
  • field width
  • conversions for strings, decimal integers, and floats (numbers).
  • argument size specifiers. These are all accepted but ignored, since Javascript has no notion of the physical size of an argument.

Everything else is currently unsupported, most notably: precision, unsigned numbers, non-decimal numbers, and characters.

Besides the usual POSIX conversions, this implementation supports:

  • %j: pretty-print a JSON object (using node's "inspect")
  • %r: pretty-print an Error object


First, install it:

# npm install extsprintf

Now, use it:

var mod_extsprintf = require('extsprintf');
console.log(mod_extsprintf.sprintf('hello %25s', 'world'));


hello                     world

Also supported

printf: same args as sprintf, but prints the result to stdout

fprintf: same args as sprintf, preceded by a Node stream. Prints the result to the given stream.


Last updated on 02 Nov 2021

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