JavaScript数组对象，有一个forEach方法，可枚举每一个数组元素，但并不支持类似for循环的break语法，中断循环：

[1,2,3].forEach(function(item) { // if(!item) break; 不支持});

解决办法，可抛出一个特殊异常，来中断forEach循环，原理：

var BreakException = {};try {[1, 2, 3].forEach(function(el) {console.log(el);if (el === 2) throw BreakException;});} catch (e) {if (e !== BreakException) throw e;}

也可复写forEach方法：

// 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;}}};}})();

使用

// Show the contents until you get to "2".[0,1,2,3,4].forEach(function(val) {if(val == 2)throw StopIteration;alert(val);});

总结

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