[1,2,3].forEach(function(el) {
if(el === 1) break;
});
如何在JavaScript中使用新的forEach方法实现这一点?我尝试过返回;,return false;和断裂。break崩溃,return只会继续迭代。
[1,2,3].forEach(function(el) {
if(el === 1) break;
});
如何在JavaScript中使用新的forEach方法实现这一点?我尝试过返回;,return false;和断裂。break崩溃,return只会继续迭代。
当前回答
为什么不尝试将函数包装在Promise中?
我提出这个问题的唯一原因是我在API中使用了一个函数,该函数的作用方式与forEach类似。我不希望它在找到值后继续迭代,我需要返回一些东西,所以我只需要解析Promise并以这种方式执行。
traverseTree(doc): Promise<any> {
return new Promise<any>((resolve, reject) => {
this.gridOptions.api.forEachNode((node, index) => {
//the above function is the one I want to short circuit.
if(node.data.id === doc.id) {
return resolve(node);
}
});
});
}
那么你所需要做的就是做一些事情,比如
this.traverseTree(doc).then((result) => {
this.doSomething(result);
});
我上面的例子是在typescript中,只需忽略类型。逻辑应该有助于你“打破”你的循环。
其他回答
这不是最有效的,因为你仍然循环所有元素,但我认为这可能值得考虑非常简单的:
let keepGoing = true;
things.forEach( (thing) => {
if (noMore) keepGoing = false;
if (keepGoing) {
// do things with thing
}
});
如果您想使用Dean Edward的建议并抛出StopIteration错误以跳出循环而不必捕获错误,则可以使用以下函数(最初来自此处):
// Use a closure to prevent the global namespace from be polluted.
(function() {
// Define StopIteration as part of the global scope if it
// isn't already defined.
if(typeof StopIteration == "undefined") {
StopIteration = new Error("StopIteration");
}
// The original version of Array.prototype.forEach.
var oldForEach = Array.prototype.forEach;
// If forEach actually exists, define forEach so you can
// break out of it by throwing StopIteration. Allow
// other errors will be thrown as normal.
if(oldForEach) {
Array.prototype.forEach = function() {
try {
oldForEach.apply(this, [].slice.call(arguments, 0));
}
catch(e) {
if(e !== StopIteration) {
throw e;
}
}
};
}
})();
上述代码将使您能够运行以下代码,而无需执行自己的try-catch子句:
// Show the contents until you get to "2".
[0,1,2,3,4].forEach(function(val) {
if(val == 2)
throw StopIteration;
alert(val);
});
需要记住的一点是,如果Array.prototype.forEach函数已经存在,则只会更新它。如果它还不存在,它将不会修改它。
还有一种方法:
var wageType = types.filter(function(element){
if(e.params.data.text == element.name){
return element;
}
});
console.dir(wageType);
从您的代码示例中,它看起来像Array.prototype.find,这就是您要查找的:Array.prototy.find()和Array.prototype.findIndex()
[1, 2, 3].find(function(el) {
return el === 2;
}); // returns 2
您可以创建forEach的变体,该变体允许break、continue、return甚至async/await:(用TypeScript编写的示例)
export type LoopControlOp = "break" | "continue" | ["return", any];
export type LoopFunc<T> = (value: T, index: number, array: T[])=>LoopControlOp;
Array.prototype.ForEach = function ForEach<T>(this: T[], func: LoopFunc<T>) {
for (let i = 0; i < this.length; i++) {
const controlOp = func(this[i], i, this);
if (controlOp == "break") break;
if (controlOp == "continue") continue;
if (controlOp instanceof Array) return controlOp[1];
}
};
// this variant lets you use async/await in the loop-func, with the loop "awaiting" for each entry
Array.prototype.ForEachAsync = async function ForEachAsync<T>(this: T[], func: LoopFunc<T>) {
for (let i = 0; i < this.length; i++) {
const controlOp = await func(this[i], i, this);
if (controlOp == "break") break;
if (controlOp == "continue") continue;
if (controlOp instanceof Array) return controlOp[1];
}
};
用法:
function GetCoffee() {
const cancelReason = peopleOnStreet.ForEach((person, index)=> {
if (index == 0) return "continue";
if (person.type == "friend") return "break";
if (person.type == "boss") return ["return", "nevermind"];
});
if (cancelReason) console.log("Coffee canceled because: " + cancelReason);
}