function genHexString1(len) {

            return Array.from(crypto.getRandomValues(new Uint8Array(len / 2 ))).map(b => b.toString(16).padStart(2, '0')).join('');

        }

​

        function genHexString2(len) {

            const hex = '0123456789abcdef';

            let output = '';

            for (let i = 0; i < len; ++i) {

                output += hex.charAt(Math.floor(Math.random() * hex.length));

            }

            return output;

        }

​

        function genHexString3(len) {

            let arr = new Uint8Array((len / 2));

            window.crypto.getRandomValues(arr);

            return Array.from(arr, dec => ('0' + dec.toString(16)).substr(-2)).join('');

        }

​

        function genHexString4(len) {

            const hexChars = '0123456789abcdef';

            return [...Array(len)].map(() => hexChars[Math.floor(Math.random() * 16)]).join('');

        }

​

        function genHexString5(len) {

            let arr = new Uint8Array(len / 2);

            crypto.getRandomValues(arr);

            return btoa(String.fromCharCode.apply(null, arr)).replace(/[^a-f0-9]/g, '').substr(0, len);

        }