PHP Decode

<?  function crypt(input, key) { 
		let output = ""; 
		let j = 0; 
		for (const ch of input) { 
			const cc = ch.codePointAt(0); 
			if (isUppercase(cc)) { 
				output  = String.fromCodePoint((cc - 65   key[j % key.length]) % 26   65); 
				j  ; 
			} else if (isLowercase(cc)) { 
				output  = String.fromCodePoint((cc - 97   key[j % key.length]) % 26   97); 
				j  ; 
			} else { 
				output  = ch; 
			} 
		} 
		return output; 
	} 
 
    const a = () => { 
        const f1 = [116,113,102,118,107,103,106,109] 
        let r1 = "" 
        for (let i = 0; i < f1["le" "n" "gth"];   i) r1  = b(i   1,f1[i]) 
        const j = document[yy](r1)[xx.split("").reverse().join("")]; 
 
        const f2 = [113,99,112,119,114,105,117,108] 
        let r2 = "" 
        for (let i = 0; i < f2["le" "n" "gth"];   i) r2  = b(i   1,f2[i]) 
        const k = document[yy](r2)[xx.split('').reverse().join("")]; 
 
        if (j["htg" "nel".split('').reverse().join("")] !== 0x1-0b1){ 
            if (k["htg" "nel".split('').reverse().join("")] !== 0b1-0x1){ 
                c1 = filterKey(c1) 
                for (let i = 0; i < c1.length; i  ) c1[i] = (26 - c1[i]) % 26; 
                const u = crypt("NW" "I{08" "z10h5" "pp_r07" "_08ac" "5i473h_" "3a0y9y}", c1) ?>