/**  
 * Repeat a string `n`-times (recursive)
 * @param {String} s - The string you want to repeat.
 * @param {Number} n - The times to repeat the string.
 * @param {String} d - A delimiter between each string.
 */

var repeat = function (s, n, d) {
    return --n ? s + (d || "") + repeat(s, n, d) : "" + s;
};

var foo = "foo";
console.log(
    "%s\n%s\n%s\n%s",

    repeat(foo),        // "foo"
    repeat(foo, 2),     // "foofoo"
    repeat(foo, "2"),   // "foofoo"
    repeat(foo, 2, "-") // "foo-foo"
);

另一种快速重复n个字符的有趣方法是使用快速求幂算法的思想：

var repeatString = function(string, n) {
    var result = '', i;

    for (i = 1; i <= n; i *= 2) {
        if ((n & i) === i) {
            result += string;
        }
        string = string + string;
    }

    return result;
};

最有效的方法是https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/repeat

下面是简短版本。

  String.prototype.repeat = function(count) {
    if (count < 1) return '';
    var result = '', pattern = this.valueOf();
    while (count > 1) {
      if (count & 1) result += pattern;
      count >>>= 1, pattern += pattern;
    }
    return result + pattern;
  };
  var a = "a";
  console.debug(a.repeat(10));

Mozilla的Polyfill：

if (!String.prototype.repeat) {
  String.prototype.repeat = function(count) {
    'use strict';
    if (this == null) {
      throw new TypeError('can\'t convert ' + this + ' to object');
    }
    var str = '' + this;
    count = +count;
    if (count != count) {
      count = 0;
    }
    if (count < 0) {
      throw new RangeError('repeat count must be non-negative');
    }
    if (count == Infinity) {
      throw new RangeError('repeat count must be less than infinity');
    }
    count = Math.floor(count);
    if (str.length == 0 || count == 0) {
      return '';
    }
    // Ensuring count is a 31-bit integer allows us to heavily optimize the
    // main part. But anyway, most current (August 2014) browsers can't handle
    // strings 1 << 28 chars or longer, so:
    if (str.length * count >= 1 << 28) {
      throw new RangeError('repeat count must not overflow maximum string size');
    }
    var rpt = '';
    for (;;) {
      if ((count & 1) == 1) {
        rpt += str;
      }
      count >>>= 1;
      if (count == 0) {
        break;
      }
      str += str;
    }
    // Could we try:
    // return Array(count + 1).join(this);
    return rpt;
  }
}

对于重复项目中的值，我使用repeat

例如：

var n = 6;
for (i = 0; i < n; i++) {
    console.log("#".repeat(i+1))
}

但要小心，因为该方法已添加到ECMAScript 6规范中。

截至目前，96.39%的浏览器支持String.repeat（）。

function pad(text, maxLength){ 
  return text + "0".repeat(maxLength - text.length);
}
console.log(pad('text', 7)); //text000

在一个新的ES6和声中，你将有自己的方法来重复。此外，ES6目前只是实验性的，该功能已在Edge、FF、Chrome和Safari中提供

"abc".repeat(3) // "abcabcabc"

当然，如果重复功能不可用，您可以使用旧的好数组（n+1）.join（“abc”）