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……
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).
从ES 2015开始，Array.prototype.find()就提供了这个确切的功能。
对于不支持此功能的浏览器，Mozilla开发者网络提供了一个填充(粘贴在下面):
if (!Array.prototype.find) {
Array.prototype.find = function(predicate) {
if (this === null) {
throw new TypeError('Array.prototype.find called on null or undefined');
}
if (typeof predicate !== 'function') {
throw new TypeError('predicate must be a function');
}
var list = Object(this);
var length = list.length >>> 0;
var thisArg = arguments[1];
var value;
for (var i = 0; i < length; i++) {
value = list[i];
if (predicate.call(thisArg, value, i, list)) {
return value;
}
}
return undefined;
};
}
