index.js

var hasMap = typeof Map === 'function' && Map.prototype;
var mapSizeDescriptor = Object.getOwnPropertyDescriptor && hasMap ? Object.getOwnPropertyDescriptor(Map.prototype, 'size') : null;
var mapSize = hasMap && mapSizeDescriptor && typeof mapSizeDescriptor.get === 'function' ? mapSizeDescriptor.get : null;
var mapForEach = hasMap && Map.prototype.forEach;
var hasSet = typeof Set === 'function' && Set.prototype;
var setSizeDescriptor = Object.getOwnPropertyDescriptor && hasSet ? Object.getOwnPropertyDescriptor(Set.prototype, 'size') : null;
var setSize = hasSet && setSizeDescriptor && typeof setSizeDescriptor.get === 'function' ? setSizeDescriptor.get : null;
var setForEach = hasSet && Set.prototype.forEach;
var hasWeakMap = typeof WeakMap === 'function' && WeakMap.prototype;
var weakMapHas = hasWeakMap ? WeakMap.prototype.has : null;
var hasWeakSet = typeof WeakSet === 'function' && WeakSet.prototype;
var weakSetHas = hasWeakSet ? WeakSet.prototype.has : null;
var booleanValueOf = Boolean.prototype.valueOf;
var objectToString = Object.prototype.toString;
var match = String.prototype.match;
var bigIntValueOf = typeof BigInt === 'function' ? BigInt.prototype.valueOf : null;

var inspectCustom = require('./util.inspect').custom;
var inspectSymbol = inspectCustom && isSymbol(inspectCustom) ? inspectCustom : null;

module.exports = function inspect_(obj, options, depth, seen) {
    var opts = options || {};

    if (has(opts, 'quoteStyle') && (opts.quoteStyle !== 'single' && opts.quoteStyle !== 'double')) {
        throw new TypeError('option "quoteStyle" must be "single" or "double"');
    }

    if (typeof obj === 'undefined') {
        return 'undefined';
    }
    if (obj === null) {
        return 'null';
    }
    if (typeof obj === 'boolean') {
        return obj ? 'true' : 'false';
    }

    if (typeof obj === 'string') {
        return inspectString(obj, opts);
    }
    if (typeof obj === 'number') {
        if (obj === 0) {
            return Infinity / obj > 0 ? '0' : '-0';
        }
        return String(obj);
    }
    if (typeof obj === 'bigint') { // eslint-disable-line valid-typeof
        return String(obj) + 'n';
    }

    var maxDepth = typeof opts.depth === 'undefined' ? 5 : opts.depth;
    if (typeof depth === 'undefined') { depth = 0; }
    if (depth >= maxDepth && maxDepth > 0 && typeof obj === 'object') {
        return '[Object]';
    }

    if (typeof seen === 'undefined') {
        seen = [];
    } else if (indexOf(seen, obj) >= 0) {
        return '[Circular]';
    }

    function inspect(value, from) {
        if (from) {
            seen = seen.slice();
            seen.push(from);
        }
        return inspect_(value, opts, depth + 1, seen);
    }

    if (typeof obj === 'function') {
        var name = nameOf(obj);
        return '[Function' + (name ? ': ' + name : '') + ']';
    }
    if (isSymbol(obj)) {
        var symString = Symbol.prototype.toString.call(obj);
        return typeof obj === 'object' ? markBoxed(symString) : symString;
    }
    if (isElement(obj)) {
        var s = '<' + String(obj.nodeName).toLowerCase();
        var attrs = obj.attributes || [];
        for (var i = 0; i < attrs.length; i++) {
            s += ' ' + attrs[i].name + '=' + wrapQuotes(quote(attrs[i].value), 'double', opts);
        }
        s += '>';
        if (obj.childNodes && obj.childNodes.length) { s += '...'; }
        s += '</' + String(obj.nodeName).toLowerCase() + '>';
        return s;
    }
    if (isArray(obj)) {
        if (obj.length === 0) { return '[]'; }
        return '[ ' + arrObjKeys(obj, inspect).join(', ') + ' ]';
    }
    if (isError(obj)) {
        var parts = arrObjKeys(obj, inspect);
        if (parts.length === 0) { return '[' + String(obj) + ']'; }
        return '{ [' + String(obj) + '] ' + parts.join(', ') + ' }';
    }
    if (typeof obj === 'object') {
        if (inspectSymbol && typeof obj[inspectSymbol] === 'function') {
            return obj[inspectSymbol]();
        } else if (typeof obj.inspect === 'function') {
            return obj.inspect();
        }
    }
    if (isMap(obj)) {
        var mapParts = [];
        mapForEach.call(obj, function (value, key) {
            mapParts.push(inspect(key, obj) + ' => ' + inspect(value, obj));
        });
        return collectionOf('Map', mapSize.call(obj), mapParts);
    }
    if (isSet(obj)) {
        var setParts = [];
        setForEach.call(obj, function (value) {
            setParts.push(inspect(value, obj));
        });
        return collectionOf('Set', setSize.call(obj), setParts);
    }
    if (isWeakMap(obj)) {
        return weakCollectionOf('WeakMap');
    }
    if (isWeakSet(obj)) {
        return weakCollectionOf('WeakSet');
    }
    if (isNumber(obj)) {
        return markBoxed(inspect(Number(obj)));
    }
    if (isBigInt(obj)) {
        return markBoxed(inspect(bigIntValueOf.call(obj)));
    }
    if (isBoolean(obj)) {
        return markBoxed(booleanValueOf.call(obj));
    }
    if (isString(obj)) {
        return markBoxed(inspect(String(obj)));
    }
    if (!isDate(obj) && !isRegExp(obj)) {
        var xs = arrObjKeys(obj, inspect);
        if (xs.length === 0) { return '{}'; }
        return '{ ' + xs.join(', ') + ' }';
    }
    return String(obj);
};

function wrapQuotes(s, defaultStyle, opts) {
    var quoteChar = (opts.quoteStyle || defaultStyle) === 'double' ? '"' : "'";
    return quoteChar + s + quoteChar;
}

function quote(s) {
    return String(s).replace(/"/g, '&quot;');
}

function isArray(obj) { return toStr(obj) === '[object Array]'; }
function isDate(obj) { return toStr(obj) === '[object Date]'; }
function isRegExp(obj) { return toStr(obj) === '[object RegExp]'; }
function isError(obj) { return toStr(obj) === '[object Error]'; }
function isSymbol(obj) { return toStr(obj) === '[object Symbol]'; }
function isString(obj) { return toStr(obj) === '[object String]'; }
function isNumber(obj) { return toStr(obj) === '[object Number]'; }
function isBigInt(obj) { return toStr(obj) === '[object BigInt]'; }
function isBoolean(obj) { return toStr(obj) === '[object Boolean]'; }

var hasOwn = Object.prototype.hasOwnProperty || function (key) { return key in this; };
function has(obj, key) {
    return hasOwn.call(obj, key);
}

function toStr(obj) {
    return objectToString.call(obj);
}

function nameOf(f) {
    if (f.name) { return f.name; }
    var m = match.call(f, /^function\s*([\w$]+)/);
    if (m) { return m[1]; }
    return null;
}

function indexOf(xs, x) {
    if (xs.indexOf) { return xs.indexOf(x); }
    for (var i = 0, l = xs.length; i < l; i++) {
        if (xs[i] === x) { return i; }
    }
    return -1;
}

function isMap(x) {
    if (!mapSize || !x || typeof x !== 'object') {
        return false;
    }
    try {
        mapSize.call(x);
        try {
            setSize.call(x);
        } catch (s) {
            return true;
        }
        return x instanceof Map; // core-js workaround, pre-v2.5.0
    } catch (e) {}
    return false;
}

function isWeakMap(x) {
    if (!weakMapHas || !x || typeof x !== 'object') {
        return false;
    }
    try {
        weakMapHas.call(x, weakMapHas);
        try {
            weakSetHas.call(x, weakSetHas);
        } catch (s) {
            return true;
        }
        return x instanceof WeakMap; // core-js workaround, pre-v2.5.0
    } catch (e) {}
    return false;
}

function isSet(x) {
    if (!setSize || !x || typeof x !== 'object') {
        return false;
    }
    try {
        setSize.call(x);
        try {
            mapSize.call(x);
        } catch (m) {
            return true;
        }
        return x instanceof Set; // core-js workaround, pre-v2.5.0
    } catch (e) {}
    return false;
}

function isWeakSet(x) {
    if (!weakSetHas || !x || typeof x !== 'object') {
        return false;
    }
    try {
        weakSetHas.call(x, weakSetHas);
        try {
            weakMapHas.call(x, weakMapHas);
        } catch (s) {
            return true;
        }
        return x instanceof WeakSet; // core-js workaround, pre-v2.5.0
    } catch (e) {}
    return false;
}

function isElement(x) {
    if (!x || typeof x !== 'object') { return false; }
    if (typeof HTMLElement !== 'undefined' && x instanceof HTMLElement) {
        return true;
    }
    return typeof x.nodeName === 'string' && typeof x.getAttribute === 'function';
}

function inspectString(str, opts) {
    // eslint-disable-next-line no-control-regex
    var s = str.replace(/(['\\])/g, '\\$1').replace(/[\x00-\x1f]/g, lowbyte);
    return wrapQuotes(s, 'single', opts);
}

function lowbyte(c) {
    var n = c.charCodeAt(0);
    var x = {
        8: 'b', 9: 't', 10: 'n', 12: 'f', 13: 'r'
    }[n];
    if (x) { return '\\' + x; }
    return '\\x' + (n < 0x10 ? '0' : '') + n.toString(16);
}

function markBoxed(str) {
    return 'Object(' + str + ')';
}

function weakCollectionOf(type) {
    return type + ' { ? }';
}

function collectionOf(type, size, entries) {
    return type + ' (' + size + ') {' + entries.join(', ') + '}';
}

function arrObjKeys(obj, inspect) {
    var isArr = isArray(obj);
    var xs = [];
    if (isArr) {
        xs.length = obj.length;
        for (var i = 0; i < obj.length; i++) {
            xs[i] = has(obj, i) ? inspect(obj[i], obj) : '';
        }
    }
    for (var key in obj) { // eslint-disable-line no-restricted-syntax
        if (!has(obj, key)) { continue; } // eslint-disable-line no-restricted-syntax, no-continue
        if (isArr && String(Number(key)) === key && key < obj.length) { continue; } // eslint-disable-line no-restricted-syntax, no-continue
        if ((/[^\w$]/).test(key)) {
            xs.push(inspect(key, obj) + ': ' + inspect(obj[key], obj));
        } else {
            xs.push(key + ': ' + inspect(obj[key], obj));
        }
    }
    return xs;
}