npm

[itboos]

###npm 一些小的工具包的源码学习:
repeat-string
(https://github.com/jonschlinkert/repeat-string)

 /*!
 * repeat-string <https://github.com/jonschlinkert/repeat-string>
 *
 * Copyright (c) 2014-2015, Jon Schlinkert.
 * Licensed under the MIT License.
 */

'use strict';

/**
 * Results cache
 */

var res = '';
var cache;

/**
 * Expose `repeat`
 */

module.exports = repeat;

/**
 * Repeat the given `string` the specified `number`
 * of times.
 *
 * **Example:**
 *
 * ```js
 * var repeat = require('repeat-string');
 * repeat('A', 5);
 * //=> AAAAA
 * ```
 *
 * @param {String} `string` The string to repeat
 * @param {Number} `number` The number of times to repeat the string
 * @return {String} Repeated string
 * @api public
 */

function repeat(str, num) {
  if (typeof str !== 'string') {
    throw new TypeError('expected a string');
  }

  // cover common, quick use cases
  if (num === 1) return str;
  if (num === 2) return str + str;

  var max = str.length * num; 
  if (cache !== str || typeof cache === 'undefined') {
    cache = str;
    res = '';
  } else if (res.length >= max) {
    return res.substr(0, max);
  }
  while (max > res.length && num > 1) {
    if (num & 1) { // 是奇数, 奇数与奇数 & 为奇数， 与偶数 2 & 1  = 0  位操作的目的是效率更高
      res += str;
    }

    num >>= 1; // num / 2 ( 等于num整除2 )
    str += str;
  }

  res += str;
  res = res.substr(0, max);
  return res;
}

参考链接:
https://stackoverflow.com/questions/4115045/ruby-what-does-the-snippet-num-1-0-exactly-do