javascript - 如何在数组中获取唯一值(How to get unique values in an array)

Question

How can I get a list of unique values in an array?(如何获得数组中唯一值的列表？)

Do I always have to use a second array or is there something similar to java's hashmap in JavaScript?(我是否总是必须使用第二个数组，或者是否有类似于JavaScript中Java哈希表的东西？)

I am going to be using JavaScript and jQuery only.(我将仅使用JavaScript和jQuery 。)

No additional libraries can be used.(不能使用其他库。)   ask by Astronaut translate from so

Answer 1

Or for those looking for a one-liner (simple and functional), compatible with current browsers :(或对于那些希望与当前浏览器兼容的单行（简单和功能性）的用户：)

 let a = ["1", "1", "2", "3", "3", "1"]; let unique = a.filter((item, i, ar) => ar.indexOf(item) === i); console.log(unique); 

Update 18-04-2017(更新18-04-2017)

It appears as though 'Array.prototype.includes' now has widespread support in the latest versions of the mainline browsers ( compatibility )(似乎“ Array.prototype.includes”现在在最新版本的主线浏览器中得到了广泛的支持（ 兼容性 ）)

Update 29-07-2015:(更新29-07-2015：)

There are plans in the works for browsers to support a standardized 'Array.prototype.includes' method, which although does not directly answer this question;(在工作中，浏览器计划支持标准的“ Array.prototype.includes”方法，尽管该方法不能直接回答此问题；)

is often related.(通常是相关的。)

Usage:(用法：)

["1", "1", "2", "3", "3", "1"].includes("2");     // true

Pollyfill ( browser support , source from mozilla ):(Pollyfill（ 浏览器支持 ， 源于mozilla ）：)

// https://tc39.github.io/ecma262/#sec-array.prototype.includes
if (!Array.prototype.includes) {
  Object.defineProperty(Array.prototype, 'includes', {
    value: function(searchElement, fromIndex) {

      // 1. Let O be ? ToObject(this value).
      if (this == null) {
        throw new TypeError('"this" is null or not defined');
      }

      var o = Object(this);

      // 2. Let len be ? ToLength(? Get(O, "length")).
      var len = o.length >>> 0;

      // 3. If len is 0, return false.
      if (len === 0) {
        return false;
      }

      // 4. Let n be ? ToInteger(fromIndex).
      //    (If fromIndex is undefined, this step produces the value 0.)
      var n = fromIndex | 0;

      // 5. If n ≥ 0, then
      //  a. Let k be n.
      // 6. Else n < 0,
      //  a. Let k be len + n.
      //  b. If k < 0, let k be 0.
      var k = Math.max(n >= 0 ? n : len - Math.abs(n), 0);

      // 7. Repeat, while k < len
      while (k < len) {
        // a. Let elementK be the result of ? Get(O, ! ToString(k)).
        // b. If SameValueZero(searchElement, elementK) is true, return true.
        // c. Increase k by 1.
        // NOTE: === provides the correct "SameValueZero" comparison needed here.
        if (o[k] === searchElement) {
          return true;
        }
        k++;
      }

      // 8. Return false
      return false;
    }
  });
}