JavaScript使用类似break机制中断forEach循环

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);

});

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