There’s no built-in ability to break in forEach. To interrupt execution you would have to throw an exception of some sort. eg.

var BreakException = {};

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

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JavaScript exceptions aren’t terribly pretty. A traditional for loop might be more appropriate if you really need to break inside it.
Use Array#some

Instead, use Array#some:

[1, 2, 3].some(function(el) {
console.log(el);
return el === 2;
});

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This works because some returns true as soon as any of the callbacks, executed in array order, return true, short-circuiting the execution of the rest.

some, its inverse every (which will stop on a return false), and forEach are all ECMAScript Fifth Edition methods which will need to be added to the Array.prototype on browsers where they’re missing.