@jsonjoy.com/util/lib/json-size/jsonSizeFast.js

Various helper utilities

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.jsonSizeFast = void 0;
const arraySize = (arr) => {
    let size = 2;
    for (let i = arr.length - 1; i >= 0; i--)
        size += (0, exports.jsonSizeFast)(arr[i]);
    return size;
};
const objectSize = (obj) => {
    let size = 2;
    for (const key in obj)
        if (
        // biome-ignore lint: .hasOwnProperty access is intentional
        obj.hasOwnProperty(key))
            size += 2 + key.length + (0, exports.jsonSizeFast)(obj[key]);
    return size;
};
/**
 * This function is the fastest way to approximate size of JSON object in bytes.
 *
 * It uses the following heuristics:
 *
 * - Boolean: 1 byte.
 * - Null: 1 byte.
 * - Number: 9 bytes (1 byte to store the number type, 8 bytes to store the number).
 * - String: 4 bytes + string length. String length is encoded in UTF-8, so it is not
 *   exactly the same as the number of bytes in the string.
 * - Array: 2 bytes + sum of sizes of elements.
 * - Object: 2 bytes + 2 bytes for each key + length of each key + sum of sizes of values.
 *
 * Rationale:
 *
 * - Booleans and `null` are stored as one byte in MessagePack.
 * - Maximum size of a number in MessagePack is 9 bytes (1 byte for the type,
 *   8 bytes for the number).
 * - Maximum overhead for string storage is 4 bytes in MessagePack. We use that, especially
 *   because we approximate the size of strings in UTF-8, which can consume more bytes if
 *   non-ASCII characters are present.
 * - Maximum overhead for arrays is 4 bytes in MessagePack, but we use 2 bytes for the
 *   array length, as we don't expect most arrays to be longer than 65,535 elements.
 * - Maximum overhead for objects is 4 bytes in MessagePack, but we use 2 bytes for the
 *   object length, as we don't expect most objects to have more than 65,535 keys.
 * - For object keys we use 2 bytes overhead for each key, as we don't expect most
 *   keys to be longer than 65,535 characters.
 *
 * @param value JSON value to calculate approximate size of
 * @returns Number of bytes required to store the JSON value
 */
const jsonSizeFast = (value) => {
    if (value === null)
        return 1;
    switch (typeof value) {
        case 'number':
            return 9;
        case 'string':
            return 4 + value.length;
        case 'boolean':
            return 1;
    }
    if (value instanceof Array)
        return arraySize(value);
    return objectSize(value);
};
exports.jsonSizeFast = jsonSizeFast;