我想知道是否有一个已知的，内置/优雅的方法来找到一个JS数组的第一个元素匹配给定的条件。c#的等效程序是List.Find。
到目前为止，我一直在使用这样的双功能组合:
// Returns the first element of an array that satisfies given predicate
Array.prototype.findFirst = function (predicateCallback) {
if (typeof predicateCallback !== 'function') {
return undefined;
}
for (var i = 0; i < arr.length; i++) {
if (i in this && predicateCallback(this[i])) return this[i];
}
return undefined;
};
// Check if element is not undefined && not null
isNotNullNorUndefined = function (o) {
return (typeof (o) !== 'undefined' && o !== null);
};
然后我可以用:
var result = someArray.findFirst(isNotNullNorUndefined);
但既然ECMAScript中有这么多函数风格的数组方法，也许已经有这样的东西了?我想很多人都必须实现这样的东西……
一种不太优雅的方法是抛出所有正确的错误消息(基于Array.prototype.filter)，但将停止对第一个结果的迭代
function findFirst(arr, test, context) {
var Result = function (v, i) {this.value = v; this.index = i;};
try {
Array.prototype.filter.call(arr, function (v, i, a) {
if (test(v, i, a)) throw new Result(v, i);
}, context);
} catch (e) {
if (e instanceof Result) return e;
throw e;
}
}
接下来的例子是
findFirst([-2, -1, 0, 1, 2, 3], function (e) {return e > 1 && e % 2;});
// Result {value: 3, index: 5}
findFirst([0, 1, 2, 3], 0); // bad function param
// TypeError: number is not a function
findFirst(0, function () {return true;}); // bad arr param
// undefined
findFirst([1], function (e) {return 0;}); // no match
// undefined
它通过使用throw结束过滤器来工作。
我从互联网上的多个来源获得灵感，推导出下面的解决方案。希望考虑到一些默认值，并提供一种方法来比较每个条目的通用方法，这就解决了。
用法:(给出值“秒”)
var defaultItemValue = { id: -1, name: "Undefined" };
var containers: Container[] = [{ id: 1, name: "First" }, { id: 2, name: "Second" }];
GetContainer(2).name;
实现:
class Container {
id: number;
name: string;
}
public GetContainer(containerId: number): Container {
var comparator = (item: Container): boolean => {
return item.id == containerId;
};
return this.Get<Container>(this.containers, comparator, this.defaultItemValue);
}
private Get<T>(array: T[], comparator: (item: T) => boolean, defaultValue: T): T {
var found: T = null;
array.some(function(element, index) {
if (comparator(element)) {
found = element;
return true;
}
});
if (!found) {
found = defaultValue;
}
return found;
}
从ECMAScript 6开始，你可以使用Array.prototype.find。这可以在Firefox(25.0)、Chrome(45.0)、Edge(12)和Safari(7.1)中实现，但不能在Internet Explorer或其他一堆旧的或不常见的平台上实现。
例如，下面的x为106:
Const x =[100,101,102,103,104,105,106,107,108,109]。Find (function (el) {
返回el > 105;
})；
console.log (x);
If you want to use this right now but need support for IE or other unsupporting browsers, you can use a shim. I recommend the es6-shim. MDN also offers a shim if for some reason you don't want to put the whole es6-shim into your project. For maximum compatibility you want the es6-shim, because unlike the MDN version it detects buggy native implementations of find and overwrites them (see the comment that begins "Work around bugs in Array#find and Array#findIndex" and the lines immediately following it).
