下面是一个稍微修改的版本，它使用Object来存储哈希，可以处理数组中的数字和字符串。

function arrDiff(a, b) {
  const hash = {};
  a.forEach(n => { hash[n] = n; });
  b.forEach(n => {
    if (hash[n]) {
      delete hash[n];
    } else {
      hash[n] = n;
    }
  });
  return Object.values(hash);
}

下面是另一个可以返回差异的解决方案，就像git diff一样:(它已经用typescript编写，如果你不使用typescript版本，只需删除类型)

/**
 * util function to calculate the difference between two arrays (pay attention to 'from' and 'to'),
 * it would return the mutations from 'from' to 'to' 
 * @param { T[] } from
 * @param { T[] } to
 * @returns { { [x in string]: boolean } } it would return the stringified version of array element, true means added,
 * false means removed
 */
export function arrDiff<T>(from: T[], to: T[]): { [x in string]: boolean } {

  var diff: { [x in string]: boolean } = {};
  var newItems: T[] = []
  diff = from.reduce((a, e) => ({ ...a, [JSON.stringify(e)]: true }), {})

  for (var i = 0; i < to.length; i++) {
    if (diff[JSON.stringify(to[i])]) {
      delete diff[JSON.stringify(to[i])]
    } else {
      newItems.push(to[i])
    }
  }

  return {
    ...Object.keys(diff).reduce((a, e) => ({ ...a, [e]: false }), {}),
    ...newItems.reduce((a, e) => ({ ...a, [JSON.stringify(e)]: true }), {})
  }
}

下面是一个用法示例:

arrDiff(['a', 'b', 'c'], ['a', 'd', 'c', 'f']) //{"b": false, "d": true, "f": true}

困难的方法(如果你想做一些比.indexOf更奇特的东西)

var difference = function (source, target) {
    return source.reduce(function (diff, current) { 
        if (target.indexOf(current) === -1) { 
            diff.push(current); 
        }

        return diff; 
    }, []);
}

简单的方法

var difference = function (source, target) {
    return source.filter(function (current) {
        return target.indexOf(current) === -1;
    });
}

const a1 = ['a', 'b', 'c', 'd'];
const a2 = ['a', 'b'];

const diffArr = a1.filter(o => !a2.includes(o));

console.log(diffArr);

输出:

[ 'a', 'b' ]

还有另一个答案，但似乎没有人提到jsperf，他们比较了几种算法和技术支持:https://jsperf.com/array-difference-javascript似乎使用过滤器得到了最好的结果。谢谢

function diff(arr1, arr2) {
  var filteredArr1 = arr1.filter(function(ele) {
    return arr2.indexOf(ele) == -1;
  });

  var filteredArr2 = arr2.filter(function(ele) {
    return arr1.indexOf(ele) == -1;
  });
  return filteredArr1.concat(filteredArr2);
}

diff([1, "calf", 3, "piglet"], [1, "calf", 3, 4]); // Log ["piglet",4]