Which is a best way to check if a variable is a function?
var cb = function () {
return;
}
if (!!(cb && cb.constructor && cb.apply)) {
cb.apply(somevar, [err, res]);
}
//VS
if (!!(cb && 'function' === typeof cb) {
cb.apply(somevar, [err, res]);
}
The most common way would be to use:
(typeof foo === 'function')
But if you want to match function-like objects (which are uncommon, but can be useful), you can check whether the object is invokable:
(foo && foo.call && foo.apply)
In most cases, you can also test the constructor (very similar to typeof):
(foo.constructor === Function)
If you want to provoke an exception, you can always:
try {
foo();
} catch (e) {
// TypeError: foo is not a function
}
I'd say the second one since it's the simplest, most intuitive and works .
if(typeof cb == 'function') { ... }