# strmid.mjs

    import isestr from './isestr.mjs'
    import isp0int from './isp0int.mjs'
    import ispint from './ispint.mjs'
    import cint from './cint.mjs'

    /**
     * 取字串中位置s開始後n個字元
     *
     * Unit Test: {@link https://github.com/yuda-lyu/wsemi/blob/master/test/strmid.test.mjs Github}
     * @memberOf wsemi
     * @param {String} c 輸入要被取的字串
     * @param {Integer} s 輸入要由第s個位置開始，為正整數
     * @param {Integer} [n=1] 輸入開始後n個字元，為正整數，預設1
     * @returns {String} 回傳處理後字串
     * @example
     *
     * console.log(strmid('test中文', 2, 1))
     * // => 's'
     *
     * console.log(strmid('test中文', 2, 3))
     * // => 'st中'
     *
     */
    function strmid(c, s, n = 1) {

        //check
        if (!isestr(c)) {
            return ''
        }
        if (!isp0int(s)) {
            return ''
        }
        if (!ispint(n)) {
            n = 1
        }
        else {
            n = cint(n)
        }

        return c.substring(s, (s + n))
    }

    export default strmid