Latest from the Rocketship
We like writing about our personal experiences, our challenges and our take on programming and management. Enjoy!
How to handle 401 unauthorized error in a Redux React application
In response to a client request, the server may return a 401 Unauthorized error. You must correctly catch it, for example, clear the state and redirect to the authorization page. To solve this problem, we wrote a custom Middleware which, in our opinion, is the best solution.
import * as actions from 'actions';
const authInterceptor = ({ dispatch }) => (next) => (action) => {
if (action.status === 401) {
dispatch(actions.removeJwt());
} else {
next(action);
}
};
Managing a Remote Development Team
Benefits of Custom Software
Deploy AnyCable with Capistrano and systemd
Integrate Drawer inside Stack Navigation in React Native
I wanted to use more than one navigation in a React Native app.
The documentation didn’t give a clear way to implement this.
Here is what you can do on purpose to add several types of navigation in your React Native app:
import { createStackNavigator, createDrawerNavigator } from 'react-navigation';
import * as Screens from './screens/index';
import Drawer from './components/DrawerMenu';
import getDrawerWidth from './utils/scale';
const AppStackNavigator = createStackNavigator({
home: {
screen: Screens.MainScreen,
},
about: {
screen: Screens.AboutScreen,
},
});
const AppNavigator = createDrawerNavigator(
{
home: {
screen: AppStackNavigator,
},
},
{
contentComponent: Drawer,
drawerWidth: getDrawerWidth,
headerMode: 'none',
}
);
export default AppNavigator;
How to add a line break to PostgreSQL?
You have to insert some data into your PostgreSQL table that has line break. As a result, the cell will look like this:
First line
Second line
To use "escape sequences" in a string literal you need to use an "extended" constant. You can specify the escape character by prefixing the letter E:
UPDATE posts SET body = E'First Line\nSecond line.' WHERE id = 2701;
What is MVP and why it is crucial to product success.
Handling IP addresses using PostgreSQL
PostgreSQL provides a inet and cidr datatypes for storing net addresses and proceed operations with them.
Host address and it's subnet can be stored with inet, while cidr can contain only network address:
select inet '192.168.0.1/24';
inet
----------------
192.168.0.1/24
select cidr '192.168.0.0/24'; -- valid cidr
cidr
----------------
192.168.0.0/24
select cidr '192.168.0.1/24'; -- invalid: cidr must not be a host address
ERROR: invalid cidr value: "192.168.0.1/24"
LINE 1: select cidr '192.168.0.1/24';
^
DETAIL: Value has bits set to right of mask.
In case there's no number after slash in cidr address the netmask is to equal 32:
select cidr('127.0.0.1');
cidr
--------------
127.0.0.1/32
The value above represents a subnet address, while the same value passed to inet represents a host:
select inet('127.0.0.1');
inet
-----------
127.0.0.1
Checking inclusion or equality can be performed with >>= and <<= operators:
select inet '192.168.0.1/24' >>= inet '192.168.0.0'; -- returns true
select cidr '192.168.0.0/24' >>= inet '192.168.0.0/12'; -- returns false
select cidr '192.168.0.0' >>= cidr '192.168.0.0'; -- returns true
And getting a netmask by a net address can be performed with netmask:
select netmask(inet('192.168.0.0/24')); -- returns 255.255.255.0
select netmask(cidr('127.0.0.1')); -- returns 255.255.255.255
JS: Parsing URL
So far, I have used the indexOf operator or regular expressions to get query string values. Today I learned how to make it easier using the URLSearchParams API:
// Assuming "?post=1234&action=edit"
let urlParams = new URLSearchParams(window.location.search);
console.log(urlParams.has('post')); // true
console.log(urlParams.get('action')); // "edit"
console.log(urlParams.getAll('action')); // ["edit"]
console.log(urlParams.toString()); // "?post=1234&action=edit"
console.log(urlParams.append('active', '1')); // "?post=1234&action=edit&active=1"
Important: Does not work in IE
Typeahead async requests throttling
As everybody else have some legacy code (who does not have it?), and yesterday we faced with problem.
Our internal app have search panel where users could write and get related results. But search was written with typeahead and without any throttling. So it's triggered full text search on backend side on every input change which leads to DB connection pool exhaustion.
We didn't found any ready to use solutions, so we added following fix:
$input.typeahead(
{
...
},
{
...
async: true
source: (query, syncResults, asyncResults) ->
href = self.href
# Added getAsyncResults call to throttle requests:
getAsyncResults(
() ->
$.ajax(
url: href
data:
query: query
dataType: 'json'
).success(
(data, textStatus, jqXHR) ->
asyncResults(data)
)
)
})
where getAsyncResults defined before typeahead init:
# throttle is lodash function
getAsyncResults = _.throttle(((fn) ->
fn()
), 300,
{ ... })
Would be happy if someone find this simple solution helpfull.
Trick: filter falsy values out of an array?
Lets say you need to filter all falsy
0, undefined, null, false, ''(empty string), NaN
values from array.
Of course you can use following construnction:
myArray
.map(item => {
// ...
})
// Get rid of falsy values
.filter(item => item);
Since the values we don't want aren't truthy, the filter above removes those falsy items.
Did you know there's a clearer way with Boolean?
myArray
.map(item => {
// ...
})
// Get rid of falsy values
.filter(Boolean);
Add conditional properties in JS objects
How conditionaly add properties to object?
As it turned out, it's pretty simple:
const user = { id: 1, name: 'Suhomozgy Andrey' }
const position = 'Frontend Developer'
const userWithPosition = {
...user,
id: 2,
...(position && { position })
}
userWithPosition //=> { id: 2, name: 'Suhomozgy Andrey', position: 'Frontend Developer' }
Create factory with an uploaded file in Rails rspec
To create a factory with an uploaded file in Rails rspec, needs to be included ActionDispatch::TestProcess module in the rails_helper.rb file to use the #fixture_file_upload method in the factories.
# spec/rails_helper.rb
include ActionDispatch::TestProcess
In a factory, when setting the attribute value, use the method #fixture_file_upload, specifying the path and file type.
# spec/factories/import_file.rb
FactoryBot.define do
factory :import_file, class: ImportFile do
data { fixture_file_upload 'spec/fixtures/test_file.pdf', 'application/pdf' }
end
end
Get most performant function
Let's say you need to determine which function is execute faster.
Write a function that take array of functions and iterates each of them a certain number of times.
Will use the difference in performance.now() values before and after to get the total time in milliseconds each iteration running.
Play with iterations argument to get more or less reliable results.
const mostPerformantFunction = (fns, iterations = 10000) => {
const times = fns.map(fn => {
const before = performance.now();
for (let i = 0; i < iterations; i++) fn();
return performance.now() - before;
});
console.log(times);
return times.indexOf(Math.min(...times));
};
mostPerformantFunction([
() => {
[1, 2, 3, 4, 5, 6, 7, 8, 9, '10'].every(el => typeof el === 'number');
},
() => {
[1, '2', 3, 4, 5, 6, 7, 8, 9, 10].every(el => typeof el === 'number');
}
]); // 1
How to download files with Axios
A simple example using the Blob() constructor:
export function someFunction(values) {
return (dispatch) => {
...
const method = 'GET';
const url = 'http://go.api/download_file';
...
axios
.request({
url,
method,
responseType: 'blob', //important
})
.then(({ data }) => {
const downloadUrl = window.URL.createObjectURL(new Blob([data]));
const link = document.createElement('a');
link.href = downloadUrl;
link.setAttribute('download', 'file.zip'); //any other extension
document.body.appendChild(link);
link.click();
link.remove();
});
};
}
Append string to a route with a slash operator
If you need to append string to some route to build a path name you can use few ways:
Rails.root + 'foo/bar'
[Rails.root, 'foo/bar'].join('/')
"#{Rails.root}/foo/bar"
But also there is a Pathname#/ method, so you can append string to route using a slash:
Rails.root/'foo/bar' # => #<Pathname:/Users/alex/myproject/foo/bar>
Looks more readable!
Recompose withContext and getContext. Simple example
Very often for nested components you need to transfer some props of the parent. For example size. So, we have the Card component. It contains a Button component.
// App.js
<Card size="sm">
{/* ... */}
<div>
{/* ... */}
<Button size="sm" onClick={action}>Action</Button>
</div>
</Card>
The size for both components is set by the "size" parameter. In the example above, the parameter passed is indicated for both components. In order not to specify the size for the Button each time, you can use the Context to use the one specified for the Card. If you use recompose, it can be super easy:
// Card.js
import { getContext } from 'recompose';
// ...
export default withContext(
{ size: PropTypes.oneOf(['sm', 'md', 'lg']) },
({ size }) => ({ size }),
)(Card);
// App.js
import Button from './Button';
// ...
const EnhancedButton = getContext({ size: PropTypes.oneOf(['sm', 'md', 'lg']) })(Button);
AND & OR Operators Precedence
Are you still sure that && and and is the same operators? Look at this:
a = true && false
a
=> false
a = true and false
a
=> true
The same situation could be reproduced for || and or. Why? The answer lies in Ruby Operator Precedence.
The first example can be represented as:
a = (true && false)
Second:
(a = true) and false
Sort lines in the vim editor
Often when writing code, you need to sort the lines in alphabetical order. For example, in javascript, when importing a large number of modules, it is good practice to organize them alphabetically. Users of the vim editor can do this very simply. It is enough to select in the visual mode all the lines that need to be sorted and enter the command :sort. All rows are sorted!
Custom onChange in React Final Form
Let's take a case when we need to call our own function to change a state of a specific field in a form (our react final form).
Here is a way to do the exact that:
You should pass your function as a parameter and after that just call it inside of the onChange method
Example:
const FormGroupAdapter = ({ input, inputOnChange }) => {
const inputProps = {
...input,
onChange: e => {
input.onChange(e);
inputOnChange && inputOnChange(e);
}
};
return <input {...inputProps} />;
};
const handleChange = event => {
console.log("!!!", event.target.value);
};
const App = () => (
<Form
...
render={({ handleSubmit, reset, submitting, pristine, values }) => (
<form onSubmit={handleSubmit}>
<div>
<label>some label</label>
<Field
name="someField"
component={FormGroupAdapter}
inputOnChange={handleChange}
/>
</div>
...
</form>
)}
/>
);