Print

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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,
    invokeGetters:    false,
    maxArrayLength:   100,
    showAll:          false,
    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.

invokeGetters

[Boolean]
Permit print to call a property getter to display its computed value.

Invoking a getter can have unwanted side-effects, so this option is disabled by default.

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"
]

showAll

[Boolean]
Include non-enumerable properties when printing an object.

Note that inherited properties are always hidden.

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 properties of printed objects.

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

Note that alphabetisation is case-insensitive.