@polkadot/util/hex/fixLength.js

A collection of useful utilities for @polkadot

import { hexAddPrefix } from './addPrefix.js';
import { hexStripPrefix } from './stripPrefix.js';
/**
 * @name hexFixLength
 * @summary Shifts a hex string to a specific bitLength
 * @description
 * Returns a `0x` prefixed string with the specified number of bits contained in the return value. (If bitLength is -1, length checking is not done). Values with more bits are trimmed to the specified length. Input values with less bits are returned as-is by default. When `withPadding` is set, shorter values are padded with `0`.
 * @example
 * <BR>
 *
 * ```javascript
 * import { hexFixLength } from '@polkadot/util';
 *
 * console.log('fixed', hexFixLength('0x12', 16)); // => 0x12
 * console.log('fixed', hexFixLength('0x12', 16, true)); // => 0x0012
 * console.log('fixed', hexFixLength('0x0012', 8)); // => 0x12
 * ```
 */
export function hexFixLength(value, bitLength = -1, withPadding = false) {
    const strLength = Math.ceil(bitLength / 4);
    const hexLength = strLength + 2;
    return hexAddPrefix((bitLength === -1 || value.length === hexLength || (!withPadding && value.length < hexLength))
        ? hexStripPrefix(value)
        : (value.length > hexLength)
            ? hexStripPrefix(value).slice(-1 * strLength)
            : `${'0'.repeat(strLength)}${hexStripPrefix(value)}`.slice(-1 * strLength));
}