encoding.js

// As described here: http://gibson042.github.io/canonicaljson-spec/
// Probably fairly inefficient, but I really doubt it matters
export function encodeCanonicalJSON(jsonNode) {
    // Escape character | quote | backslash | high surrogate not followed by low, or low surrogate not following
    // a high surrogate
    const replaceRegex = /[\u0000-\u001F]|"|\\|[\uD800-\uDBFF](?![\uDC00-\uDFFF])|(?:[^\uD800-\uDBFF]|^)[\uDC00-\uDFFF]/g;
    const toSlashEscape = {
        "\b": "\\b",
        "\t": "\\t",
        "\n": "\\n",
        "\f": "\\f",
        "\r": "\\r",
        "\"": "\\\"",
        "\\": "\\\\",
    };
    const escapeCharacter = (character) => {
        const slashEscaped = toSlashEscape[character];
        if (slashEscaped) {
            return slashEscaped;
        } else {
            // If the character is marked for replacement and we can't slash escape it, we'll encode it
            // with a six-character \u00xx uppercase hexadecimal escape sequence
            const charCode = character.charCodeAt(0).toString(16).toUpperCase().padStart(4, "0");
            return "\\u" + charCode;
        }
    }

    const exponentialRegex = /^(\d)(?:\.(\d*))?e([+-]\d+)$/;
    const formatExponential = (number) => {
        // Must be a floating point number
        const match = number.toExponential().match(exponentialRegex);
        const integer = match[1];
        // May not include a decimal component, but we need it
        const decimal = match[2] || '0';
        // Will remove + if present
        const exponent = parseInt(match[3]);
        return `${integer}.${decimal}E${exponent}`;
    };

    const doEncode = (jsonNode, depth) => {
        if (depth > 1000) {
            throw new Error("Max depth exceeded");
        } else if (jsonNode === undefined) {
            throw new Error("Invalid type: undefined");
        } else if (jsonNode === null) {
            return "null";
        } else if (typeof jsonNode === "boolean") {
            return jsonNode.toString();
        } else if (typeof jsonNode === "number" && Number.isInteger(jsonNode)) {
            return jsonNode.toString();
        } else if (typeof jsonNode === "number") {
            return formatExponential(jsonNode);
        } else if (typeof jsonNode === "string") {
            return `"${jsonNode.replace(replaceRegex, escapeCharacter)}"`;
        } else if (typeof jsonNode === "object" && Array.isArray(jsonNode)) {
            const nodeContents = jsonNode.map((value) => encodeCanonicalJSON(value, depth + 1)).join(",");
            return `[${nodeContents}]`;
        } else if (typeof jsonNode === "object") {
           // Order the members of all objects lexicographically by the UCS (Unicode Character Set) code points of their names
           // Do not include key value pairs where their value is undefined.
           const nodeContents = Object.keys(jsonNode).sort().filter(
               key => jsonNode[key] !== undefined
           ).map(key =>
               [encodeCanonicalJSON(key, depth + 1), encodeCanonicalJSON(jsonNode[key], depth + 1)].join(":")
           ).join(",");
           return `{${nodeContents}}`;
        } else {
            throw new Error("Unknown type");
        }
    };

    return doEncode(jsonNode, 0);
}