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print

Print

Generate a human-readable representation of a value. Focussed on producing clean and accurate depictions of data. Suitable for debugging and generating diffs.

Usage

const print = require("print");
let output = print({
    foo: "bar",
    baz: "quux",
    list: [1, 2, 3, 4, "five"]
});
console.log(output);
 
print.out(obj); // Shortcut for console.log(print(obj)); 

Comparison with built-in functions

print                JSON.stringify          util.inspect
 
{                    {                       { foo: 'bar',
    baz: "quux"          "foo": "bar",         baz: 'quux',
    foo: "bar"           "baz": "quux",        list:
    list: [              "list": [             [ 1,
        1                    1,                  2,
        2                    2,                  3,
        3                    3,                  4,
        4                    4,                  'five' ] }
        "five"               "five"
    ]                    ]
}                    }

print also handles circular references by showing a -> pointing to where the object was first mentioned. For example, the following code:

const A = {};
const B = {foo: A};
print({A, B});

Will produce:

{
    A: {}
    B: {
        foo: -> A
    }
}

Options

An optional second parameter can be passed to refine print's output.

Available options and their default values are listed below:

print(input, {
    ampedSymbols:     true,
    escapeChars:      /(?!\x20)\s|\\/g,
    maxArrayLength:   100,
    showArrayIndices: false,
    showArrayLength:  false,
    sortProps:        true
});

ampedSymbols

Boolean
Prefix Symbol-keyed properties with @@. Disable to show Symbol(…) instead.

escapeChars

RegExp | Function
What characters, if any, are escaped in string values.

By default, anything that alters the output's meaning or layout is escaped:

\f \n \r \t \v \\

This can be overridden with a custom expression or callback, the latter of which receives the entire string as an argument.

Passing falsey values to escapeChars disables escaping altogether, which isn't recommended if your input contains line-breaks or tabulation.

maxArrayLength

Number
Maximum number of array values to show before truncating them:

[
    1
    2
    3
 
    … 7 more values not shown
]

Note this excludes any named properties stored on the Array object:

const input = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
input.foo = "bar";
print(input, { maxArrayLength: 3 })
[
    1
    2
    3
    
    … 7 more values not shown
 
    foo: "bar"
]

showArrayIndices

Boolean
Show the index of each element in an array.

[                  [
    "A"                0: "A"
    "B"      ->        1: "B"
    "C"                2: "C"
]                  ]

showArrayLength

Boolean
Display an array's length property after its values:

[
    "A"
    "B"
    "C"
    length: 3
]

sortProps

Boolean
Alphabetise the enumerable properties of printed objects.

To display properties in the order they were enumerated, set this to false.

Note that alphabetisation is case-insensitive.