in packages/fbjs/src/functional/flatMapArray.js [22:39]
function flatMapArray<TValue, TNext>(
array: Array<TValue>,
fn: (value: TValue, index: number) => Array<TNext>,
): Array<TNext> {
var ret = [];
for (var ii = 0; ii < array.length; ii++) {
var result = fn.call(array, array[ii], ii);
if (Array.isArray(result)) {
push.apply(ret, result);
} else if (result != null) {
throw new TypeError(
'flatMapArray: Callback must return an array or null, ' +
'received "' + result + '" instead'
);
}
}
return ret;
}