palindrome.js

function* range(a, b, pred) {
    while (a < b) {
        if (typeof pred === 'undefined' || pred(a)) {
            yield a;
        }
        ++a;
    }
}

function isPalindrome(val) {
    val = val.toString();
    const mid = val.length / 2;
    for (let off = 0; off < mid; off++) {
        if (val[val.length - 1 - off] !== val[off]) {
            return false;
        }
    }
    return true;
}

const primes = [...range(10000, 100000, a => {
    for (let x of range(2, Math.sqrt(a) + 1)) {
        if (a % x === 0) {
            return false;
        }
    }
    return true;
})].reverse();

function getExpr() {
    for (let a of primes) {
        for (let b of primes) {
            const c = a * b;
            if (isPalindrome(c)) {
                return `${a} * ${b} = ${c}`;
            }
        }
    }
}

console.time();
console.log(getExpr());
console.timeEnd();