[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

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。

其他回答

在其他网站上找到此解决方案。您可以在try/catch场景中包装forEach。

if(typeof StopIteration == "undefined") {
 StopIteration = new Error("StopIteration");
}

try {
  [1,2,3].forEach(function(el){
    alert(el);
    if(el === 1) throw StopIteration;
  });
} catch(error) { if(error != StopIteration) throw error; }

此处提供更多详细信息:http://dean.edwards.name/weblog/2006/07/enum/

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);
}

引用Array.prototype.forEach()的MDN文档:

除此之外,无法停止或中断forEach()循环通过抛出异常。如果您需要这样的行为,.forEach()方法是错误的工具,请改用普通循环。如果要测试谓词的数组元素并需要布尔返回值,则可以改用every()或some()。

对于您的代码(在问题中),如@bobince所建议的,请改用Array.protocol.some()。它非常适合您的用例。

Array.pr原型.some()对数组中的每个元素执行一次回调函数,直到找到一个回调返回真值(当转换为布尔值时变为真)的元素。如果找到这样的元素,some()立即返回true。否则,some()返回false。回调仅对已赋值数组的索引调用;对于已删除或从未赋值的索引,不会调用它。

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。

你可以按照下面的代码操作,这对我很有用:

 var     loopStop = false;
YOUR_ARRAY.forEach(function loop(){
    if(loopStop){ return; }
    if(condition){ loopStop = true; }
});