Filling string with chars N times (e.g. to test long vectors of hash functions) http://www.di-mgt.com.au/sha_testvectors.html

stringFill.js

// console.log(sha1(stringFill("a", 1000000)));

function stringFill(string, times) {
    var result = "";
    for (;;) {
        if (times & 1) result += string;
        times >>= 1;
        if (times) string += string;
        else break;
    }
    return result;
}

// alternative

function repeatString(string, times) {
    var result = "";
    while (times > 0) {
        if (times & 1) result += string;
        times >>= 1;
        string += string;
    }
    return result;
}