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;
  }
}

/**  
 * 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"
);

如果你经常重复自己的话，那么很方便：

String.prototype.repeat=String.prototype.repeat||函数（n）{n=n||1；return Array（n+1）.join（this）；}alert（'我们到了吗？\n没有。\n'。重复（10））

如果您不反对在项目中包含库，lodash有一个repeat函数。

_.repeat('*', 3);
// → '***

https://lodash.com/docs#repeat

我意识到这不是一个流行的任务，如果你需要重复字符串而不是整数次呢？

使用repeat（）和slice（）是可能的，下面是方法：

String.prototype.fracRepeat = function(n){
  if(n < 0) n = 0;
  var n_int = ~~n; // amount of whole times to repeat
  var n_frac = n - n_int; // amount of fraction times (e.g., 0.5)
  var frac_length = ~~(n_frac * this.length); // length in characters of fraction part, floored
  
  return this.repeat(n) + this.slice(0, frac_length);
}

以下是一个简短的版本：

String.prototype.fracRepeat=函数（n）{如果（n＜0）n＝0；返回this.repeat（n）+this.slice（0，~~（（n-~n）*this.length））；}var s=“abcd”；console.log（s.fracRepeat（2.5））

Array(10).fill('a').join('')

尽管投票最多的答案有点紧凑，但使用这种方法，您不必添加额外的数组项。