Function pad

apps/json-format/json-utils.js:359–364

(src, len)

// ─── 日期格式化（替代 Date.prototype.format 的纯函数版本）──
export function formatDate(date, pattern) {
    const pad = (src, len) => {
        const neg = src < 0;
        let s = String(Math.abs(src));
        while (s.length < len) s = '0' + s;
        return (neg ? '-' : '') + s;
    };
    if (typeof pattern !== 'string') return date.toString();

    const y = date.getFullYear();