Package Exports

fast-printf
fast-printf/dist/src/printf.js

This package does not declare an exports field, so the exports above have been automatically detected and optimized by JSPM instead. If any package subpath is missing, it is recommended to post an issue to the original package (fast-printf) to support the "exports" field. If that is not possible, create a JSPM override to customize the exports field for this package.

Readme

fast-printf

Fast and spec-compliant printf implementation for Node.js and browser.

Usage
Handling Unbound Value References
Benchmark
Printf Cheatsheet

Usage

import {
  printf,
} from 'fast-printf';

console.log(printf('foo %s', 'bar'));

Handling Unbound Value References

By default, interpolating an unbound expression produces:

The expression is left in place
A warning is logged using roarr

i.e. printf('%s bar') produces %s bar.

This behavior can be overridden by configuring a fast-printf instance using createPrintf:

import {
  createPrintf,
} from 'fast-printf';

const printf = createPrintf({
  formatUnboundExpression: (
    subject: string,
    token: PlaceholderToken,
    boundValues: any[],
  ): string => {
    console.warn({
      boundValues,
      position: token.position,
      subject,
    }, 'referenced unbound value');

    return token.placeholder;
  };
});

console.log(printf('foo %s', 'bar'));

Benchmark

implementation	without_placeholders	with_string_placeholder	with_many_string_placeholders
`sprintf`	31,772,029	4,154,748	637,229
`printf`	651,970	373,615	160,795
`fast-printf`	78,068,540	11,820,632	2,552,386

Results show operations per second (greater is better).

To run the benchmark yourself please see ./benchmark.

Printf Cheatsheet

// %c character
printf('%c', 'b');
// => 'c'

// %C converts to uppercase character (if not already)
printf('%C', 'b');
// => 'B'

// %d decimal integer (base 10)
printf('%d', 100);
// => '100'

// %0Xd zero-fill for X digits
printf('%05d', 1);
// => '00001'

// %Xd right justify for X digits
printf('%5d', 1);
// => '    1'

// %-Xd left justify for X digits
printf('%-5d', 1);
// => '1    '

// %+d adds plus sign(+) to positive integers, minus sign for negative integers(-)
printf('%+5d', 1);
// => '    +1'
printf('%+5d', -1);
// => '    -1'

// %e scientific notation
printf('%e', 52.8);
// => '5.28e+1'

// %E scientific notation with a capital 'E'
printf('%E', 52.8);
// => '5.28E+1'

// %f floating-point number
printf('%f', 52.8);
// => '52.8'

// %.Yf prints Y positions after decimal
printf('%.1f', 1.234);
// => '1.2'

// %Xf takes up X spaces
printf('%5f', 123);
// => '  123'

// %0X.Yf zero-fills
printf('%05.1f', 1.234);
// => '001.2'

// %-X.Yf left justifies
printf('%-5.1f', 1.234);
// => '1.2  '

// %i integer (base 10)
printf('%i', 123);
// => '123'

// %b converts to boolean
printf('%b', true);
// => 'true'
printf('%b', 'true');
// => 'true'
printf('%b', 1);
// => 'true'

// %B converts to uppercase boolean
printf('%b', true);
// => 'TRUE'
printf('%b', 'true');
// => 'TRUE'
printf('%b', 1);
// => 'TRUE'

// %o octal number (base 8)
printf('%o', 8);
// => '10'

// %s a string of characters
printf('%s', 'foo');
// => 'foo'

// %Xs formats string for a minimum of X spaces
printf('%5s', 'foo');
// => '  foo'

// %-Xs left justify
printf('%-5s', 'foo');
// => 'foo  '

// %S converts to a string of uppercase characters (if not already)
printf('%S', 'foo');
// => 'FOO'

// %u unsigned decimal integer
printf('%u', 1);
// => '1'
printf('%u', -1);
// => '4294967295'

// %x number in hexadecimal (base 16)
printf('%x', 255);
// => 'ff'

// %% prints a percent sign
printf('%%');
// => '%'

// \% prints a percent sign
printf('\\%');
// => '%'

// %2$s %1$s positional arguments
printf('%2$s %1$s', 'bar', 'foo');
// => 'foo bar'