Logging. Colors. Terminals & browsers. Show call locations. Pretty prints objects, Errors, anything!
console.log for the log-driven debugging junkiesError instances as pretty stacktraces with source linesget-source)These examples demonstrate some non-trivial complex behaviors that could be achieved with Ololog by plugging into it's rendering pipeline. For simpler examples read further docs!
Logging to a file and on screen at the same time (with different log levels)
Collapsing repeated messages (with an incrementing counter)
Displaying log levels and custom tags
For use with Node or with module bundlers (Browserify / WebPack / Rollup):
npm install ololog
const log = require ('ololog')
mocha --reporter ololog/reporter
.only or this.verbose=true for a suite/test)NOTE: It is highly experimental yet, and things may not work as expected...
...for those who still uses <script> tag for module importing ;) Exposes the global ololog and ansicolor objects. Installs String extensions for ANSI styles. Not compressed.
<script src="https://unpkg.com/ololog"></script> <!-- from unpkg.com CDN -->
<script>
log = ololog
log ('something'.red)
</script>
At first, it's similar to console.log:
log ('foo', 'bar', 'baz') // foo bar baz
It exposes a method called .configure, which produces a new log instance with the new settings applied (not mutating the original one), which can be saved and re-used subsequently:
const log = require ('ololog').configure ({ concat: { separator: '' }})
log ('foo', 'bar', 'baz') // foobarbaz
...or you can apply the configuration method ad-hoc:
log.configure ({ concat: { separator: '' }}) ('foo', 'bar', 'baz') // foobarbaz
And you can chain the configuration calls, applying them subsequently:
log1 = log.configure ({ locate: false }) // removes the code location tag
log1 ('foo')
log2 = log1.configure ({ time: true }) // preserves previous settings + enables timestamps
log2 ('bar')
The variety of possible options will be covered just below — there is a plenty of them!
Configuration engine is implemented as a separate external library, for everyone's use — you can read more about it here. Contributions are welcome.
Ololog returns its first argument (a feature that console.log doesn't have), and it greatly simplifies debugging of functional expressions, as you can simply wrap part of an expression to log:
array.map (x => log (x) + 1)
It is far less ugly than with console.log:
array.map (x => { console.log (x); return x + 1 })
Also, if you don't like that behavior, you can override it. For example, returning the last argument instead of first:
log = log.configure ({
returnValue: (text, { initialArguments }) => initialArguments[initialArguments.length - 1]
})
Backed by the ansicolor library, colored output is supported for the terminal environment and for the Chrome DevTools console. On other platforms, ANSI codes are safely stripped from the output, so they don't mess up anything.
Apply styling by calling the ansicolor methods on arbitrary strings:
require ('ansicolor').nice // importing in .nice mode extends the String prototype, but there's a safe functional mode as well (see the docs...)
log (('foo'.dim.red + 'bar'.bgLightCyan).underline)
...or by using the built-in shorthand methods (no need to import ansicolor, but we lose the ability to colorize just a part of a string):
log.red ('red text')
log.bright.red.underline ('multiple styles combined')
See all the supported styling options here.
To add indentation to a multiline text or complex objects, you can simply provide the indentation symbols as a first argument:
log (' ', 'foo\nbar\nbar')
foo
bar
bar
The remarkable thing is that you can provide any text that would be used to offset what's coming after it. This is especially useful with printing long objects that span across many lines:
log ('This is my object:', { foo: 10, bar: 20, qux: 30 })
This is my object: { foo: 10,
bar: 20,
qux: 30 }
Compare it to the crappy console.log output, which doesn't care about readability:
This is my object: { foo: 10,
bar: 20,
qux: 30 }
Ololog also handles the ANSI escape codes correctly while computing the proper the indentation width:
const { bright } = require ('ansicolor')
log.magenta (bright.green ('This is my object:'), { foo: 10, bar: 20, qux: 30 })
indent OptionThe other way is to use the indent config option:
log.configure ({ indent: { level: 3 } }) ('foo\nbar\nbaz\n')
Shorthand method:
log.indent (2) ('foo\n', 'bar\n', 'baz')
You can also set the indentation pattern should be used:
log = log.configure ({ indent: { pattern: '\t' } })
All magic is provided by the external String.ify library. Read the docs to see all the available configuration options. There are plenty of them! Contributions are welcome.
Default output:
log (obj) // prints example object
{ asks: [ { price: "1000", amt: 10 },
{ price: "2000", amt: 10 } ],
bids: [ { price: "500", amt: 10 },
{ price: "100", amt: 10 } ] }
Longer strings:
log.maxLength (70) (obj)
{ asks: [{ price: "1000", amt: 10 }, { price: "2000", amt: 10 }],
bids: [{ price: "500", amt: 10 }, { price: "100", amt: 10 }] }
Shorter strings:
log.maxLength (20) (obj)
{ asks: [ { price: "1000",
amt: 10 },
{ price: "2000",
amt: 10 } ],
bids: [ { price: "500",
amt: 10 },
{ price: "100",
amt: 10 } ] }
Disabling right keys alignment:
log.noRightAlignKeys (anotherObj)
{ obj: [ { someLongPropertyName: 1,
propertyName: 2,
anotherProp: 4,
moreProps: 5 },
{ propertyName: { someVeryLongPropertyName: true,
qux: 6,
zap: "lol" } } ] }
Disabling fancy nesting:
log.noFancy (anotherObj)
{
obj: [
{
someLongPropertyName: 1,
propertyName: 2,
anotherProp: 4,
moreProps: 5
},
{
propertyName: {
someVeryLongPropertyName: true,
qux: 6,
zap: "lol"
}
}
]
}
No fancy nesting + setting indentation width to 2 spaces:
log.configure ({ stringify: { fancy: false, indentation: ' ' } }) (yetAnotherObj)
{
obj: [
{
propertyName: 2,
moreProps: 5
}
]
}
Single line mode:
log.noPretty (obj)
{ asks: [{ price: "1000", amount: 10 }, { price: "2000", amount: 10 }], bids: [{ price: "500", amount: 10 }, { price: "100", amount: 10 }] }
Changing max print depth / max array length:
log.maxDepth (1).maxArrayLength (100) (obj) // or log.configure ({ stringify: { maxDepth: 1, maxArrayLength: 100 } })
log.unlimited (obj) // disables limiting
Setting floating-point output precision:
log.precision (2) ({ foo: 123.456789 })
{ foo: 123.45 }
Passing other configuration options to string.ify (read the its docs for more info):
log.configure ({
stringify: {
pure: false,
json: false,
maxDepth: 5,
maxLength: 50,
maxArrayLength: 60,
maxObjectLength: 200,
maxStringLength: 60,
precision: undefined,
formatter: undefined,
pretty: 'auto',
rightAlignKeys: true,
fancy: true,
indentation: ' '
}
}) (obj)
Please not that in case of multiple configuration options it is preferable to do that:
log.configure ({ stringify: { precision: 2, maxLength: 20, noFancy: true, maxDepth: 8 }})
...instead of:
log.precision (2).maxLength (20).noFancy.maxDepth (8)
...because the latter generates too deep callstack which could disrupt the displaying of the call location tag along with the message! The problem is yet to be solved in future pipez versions.
Replacing the default printer with q-i (as an example):
const log = require ('ololog').configure ({ stringify: { print: require ('q-i').stringify } })
log ({ foo: true, bar: 42 })
You can also override the arguments stringification stage completely (see more on overriding default behavior):
log = require ('ololog').configure ({ stringify (args, cfg) { return args.map (x => myCustomStringifier (x, cfg)) } })
// ...providing additional configuration somewhere later...
log = log.configure ({ stringify: { /* this object will be passed down as `cfg` to myCustomStringifier */ }})
Error InstancesThis feature is implemented in the StackTracey library. See it's docs for more (you can configure the path shortening / library calls skipping).
log.bright.red (e) // where `e` is an instance of Error
or (if you want the output go to stderr and supress the grey location badge):
log.bright.red.error.noLocate (e)
process.on ('uncaughtException', e => { log.bright.red.error.noLocate (e); process.exit (1) })
process.on ('unhandledRejection', e => { log.bright.red.error.noLocate (e); process.exit (1) })
Or you can simply call the handleNodeErrors helper when importing Ololog:
const log = require ('ololog').handleNodeErrors ()
panic-overlayYou can improve the error reporting not only in Node projects, but also in browsers. See the panic-overlay library which shares the same codebase with Ololog:
Have you ever encountered a situation where you need to quickly find in the code the place where the logging is called, but it's not so easy to do? With call location tags it's really easy. And it's enabled by default.
Disabling:
log.configure ({ locate: false }) (...)
...or:
log.noLocate (...)
Custom printer:
log.configure ({ locate: { print: ({ calleeShort, fileName, line }) => ... } }) (...)
Displaying outer call location (upwards the stack), can be useful when implementing library code / wrappers:
log.configure ({ locate: { shift: 1 }}) (...)
Manually setting call location (see the StackTracey library, which serves the purpose):
log.configure ({ locate: { where: new StackTracey ().at (2) } }) (...)
Disabled by default. To enable (with default options):
log = log.configure ({ time: true })
Configure formatting:
log = log.configure ({ time: { yes: true, format: 'iso' } })
Here is the correspondence between the format option value and the related Date method used for rendering:
format value | Date method |
|---|---|
"locale" (default) | .toLocaleString () |
"iso" | .toISOString () |
"utc" | .toUTCString () |
null | .toString () |
Providing locale and timezone options (available when format is set to locale):
log.configure ({
time: {
yes: true,
format: 'locale',
locale: 'en-US',
options: { timeZone: 'America/Denver' }
}
})
Providing a custom printer:
log.configure ({ time: { yes: true, print: x => (String (x) + ' | ').bright.cyan }}) ('Lorem ipsum dolor sit amet\nconsectetur adipiscing elit..')
Backdating:
log.configure ({ time: { yes: true, when: new Date ('2017-02-27T12:45:19.951Z') }}) (...)
You can add the .error call modifier, which tells Ololog to render with the console.error instead of the console.log:
log.error ('this goes to stderr')
log.bright.red.error ('bright red error!')
Other console methods are supported as well:
log.info ('calls console.info')
log.warn ('calls console.warn')
log.debug ('calls console.debug')
INFO / WARN / ERROR / DEBUG TagsThere is a tag stage (disabled by default) that displays the log level:
const log = require ('ololog').configure ({ tag: true })
log ('a regular message')
log.info ('an info message')
log.warn ('a warning')
log.error ('an error')
log.debug ('a debug message')
You can completely override the tag stage, introducing new parameters and behavior (a clusterId in this example):
const bullet = require ('string.bullet') // NB: these packages are part of Ololog, no need to install them separately
const { cyan, yellow, red, dim } = require ('ansicolor')
const log = require ('ololog').configure ({
locate: false,
time: true,
tag: (lines, {
level = '',
levelColor = { 'info': cyan, 'warn': yellow, 'error': red.bright.inverse, 'debug': blue},
clusterId
}) => {
const clusterStr = clusterId ? ('CLUSTER[' + (clusterId + '').padStart (2, '0') + ']') : ''
const levelStr = level && (levelColor[level] || (s => s)) (level.toUpperCase ())
return bullet (dim (clusterStr.padStart (10)) + '\t' + levelStr.padStart (6) + '\t', lines)
}
})
log.configure ({ tag: { clusterId: 1 } }) ('foo')
log.configure ({ tag: { clusterId: 3 } }).info ('bar')
log.configure ({ tag: { clusterId: 27 } }).error ('a multiline\nerror\nmessage')
The output:
You can also use Custom Methods feature to make it even more concise:
log = log.methods ({
// adds `clusterId` helper
clusterId (n) { return this.configure ({ tag: { clusterId: n } }) }
})
log.clusterId (1) ('foo')
log.clusterId (3) .info ('bar')
log.clusterId (27).error ('a multiline\nerror\nmessage')
log.configure ({ trim: { max: 5 } }) ('1234567890', 'abcdefgh') // 1234… abcd…
The following will execute all stages before the 'render' (screen output) stage, returning its argument:
log.before ('render') ({ foo: 42 }) // '{ foo: 42 }'
The other way of getting the text (for example, if you want to intercept it and output to your custom renderer, like Blessed) is to override the default render step, see below...
You can provide a custom implementation for certain steps in the Ololog's pipeline. For example, you can replace the render step to output the rendered text to somewhere else other than console.log:
log = log.configure ({
render (text, { consoleMethod = '' /* can be also debug/info/error/warn */ }) {
// receives '{ foo: 42 }' and outputs it to the Blessed library
box.pushLine (text)
box.scroll (1)
screen.render ()
}
})
log ({ foo: 42 })
You can look up all the default steps you could replace here:
https://github.com/xpl/ololog/blob/master/ololog.js#L67
You can also bind new code to the existing methods in an aspect-oriented programming style, executing it before, after or instead – and thus overriding the default behavior. See the pipez library, which provides all the fun — with its help you could build incredibly configurable things similar to Ololog easily.
For example, if you want to write .error calls not just on screen, but to a separate file, you can do following (by injecting a custom hook after the render call):
const ololog = require ('ololog')
, ansi = require ('ansicolor')
, fs = require ('fs')
const log = require ('ololog').configure ({
'render+' (text, { consoleMethod = '' }) { // adds this method after `render`
if (consoleMethod === 'error') {
fs.appendToFile ('error.log', '\n' + ansi.strip (text)) // strip ANSI styling codes from output
}
return text
}
})
Here's a complete example on how to set up a file logging that supports different log levels:
Here's another trick that you could do by injecting a handler before the render step (that would be +render instead of render+):
You can add your own shorthand methods/properties (will add new properties globally for any instance of the ololog, but this may change in future). An example, demonstrating how the actual indent and red chain-style helpers were implemented:
log.methods ({
indent (level) { return this.configure ({ indent: { level: level }}) }
get red () { return this.configure ({ 'concat+': lines => lines.map (ansicolor.red) }) } // executes it after the 'concat'
})
Use .noop to obtain a reduced instance that does nothing apart from returning its first argument:
const doesNothing = log.noop
doesNothing.bright.red ('this never shows') // simply returns 'this never shows'
FAQs
Logging. Colors. Terminals & browsers. Show call locations. Pretty prints objects, Errors, anything!
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