function forIn( obj, fcn, thisArg ) {
	var bool;
	var key;
	if ( typeof obj !== 'object' || obj === null ) {
		throw new TypeError( format( 'invalid argument. First argument must be an object. Value: `%s`.', obj ) );
	}
	if ( !isFunction( fcn ) ) {
		throw new TypeError( format( 'invalid argument. Second argument must be a function. Value: `%s`.', fcn ) );
	}
	for ( key in obj ) { // eslint-disable-line guard-for-in
		bool = fcn.call( thisArg, obj[ key ], key, obj );
		if ( bool === false ) {
			return obj;
		}
	}
	return obj;
}
Invokes a function once for each own and inherited enumerable property of an object.

## Notes

-   Iteration order is **not** guaranteed.

@param {Object} obj - input object
@param {Function} fcn - function to invoke
@param {*} [thisArg] - execution context
@throws {TypeError} first argument must be an object
@throws {TypeError} second argument must be a function
@returns {Object} obj - input object

@example
function log( v, key ) {
    console.log( '%s: %d', key, v );
}

function Foo() {
    this.a = 1;
    this.b = 2;
    return this;
}

Foo.prototype.c = 3;
Foo.prototype.d = 4;

var obj = new Foo();

forIn( obj, log );