.NET 的 LINQ 包含一个运算符 .Single
哪个
Returns the only element of a sequence, and throws an exception if there is not exactly one element in the sequence.
最新版本的 JavaScript 中是否有等效项? (撰写本文时为 ECMA v8)。
我能找到的最接近的操作是 .find
尽管人们必须编写自己的样板来断言恰好有一个元素匹配。
.single()
的预期功能示例:
const arr = [1, 4, 9];
arr.single(v => v > 8 && v < 10); // Returns 9
arr.single(v => v < 5); // Throws an exception since more than one matches
arr.single(v => v > 10); // Throws an exception since there are zero matches
最佳答案
Is there an equivalent in the latest version of JavaScript? (ECMA v8 at time of writing).
不,不是。
您可以更改 Array
的原型(prototype)(这是不可取的)并添加一个方法来过滤数组并返回单个找到的项目或抛出错误。
Array.prototype.single = function (cb) {
var r = this.filter(cb);
if (!r.length) {
throw 'zero match';
}
if (r.length !== 1) {
throw 'too much matches';
}
return r[0];
};
const arr = [1, 4, 9];
console.log(arr.single(v => v > 8 && v < 10)); // 9
console.log(arr.single(v => v < 5)); // exception since more than one matches
// console.log(arr.single(v => v > 10)); // exception since there are zero matches
或者您可以使用 link.js
.
const arr = [1, 4, 9];
console.log(Enumerable.From(arr).Single(v => v > 8 && v < 10)); // 9
console.log(Enumerable.From(arr).Single(v => v < 5)); // exception since more than one matches
// console.log(Enumerable.From(arr).Single(v => v > 10)); // exception since there are zero matches
<script src="https://cdnjs.cloudflare.com/ajax/libs/linq.js/2.2.0.2/linq.js"></script>
关于JavaScript 查找数组中的单个元素,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/50853114/