React “statePropsPrecalculationError” and TypeError ‘state’ of undefined

Debugging a React component can be a pain.

There are many causes for “statePropsPrecalculationError”, for debugging see my post on Debugging React statePropsPrecalculationError post.

When you specifically have ” ‘state’ of undefined” the fix is simple:

Recently I ran into “statePropsPrecalculationError” alongside with the the console warning TypeError: Cannot read property ‘state’ of undefined(…)`.

This is super easy to fix, but not immediately obvious. Whenever you use `this.setState()` inside your component, you must define your initial state!

Just add a `getInitialState()` definition!


const MyComponent = React.createClass({
getInitialState() {
return {
isOpen: false
};
},
toggleOpen() {
this.setState({isOpen: !this.state.isOpen});
},
render() {
return (

Hello World!

);
}
});

LoDash.js / Underscore.js mixins

Here are a few mixins I’ve created for LoDash.js I’ve found handy.

_.getDeep

/**
* Safely retrieves the value of a deeply nested object value
* @param {object} O The Object to be searched
* @param {string} str Dot notation string of the address of the attribute to be retrieved
* @return {mixed} Value of nested item or undefined
* @link http://stackoverflow.com/a/15400575/417822
*/
_.mixin({'getDeep': function(O, str) {
if ( !_.isObject(O) ) return;

var seg= str.split('.');
while(O && seg.length) {
O = O[seg.shift()];
}
return O;
}});

_.hasDeep

/**
* Tests if a deep value has a value/exists. Uses _.getDeep to retrieve value.
* @param {object} O The Object to be tested
* @param {string} str Dot notation string of the address of the attributed to be tested
* @return {boolean}
* @todo validate that falesy values 'false' '0' etc come back as true.
*/
_.mixin({'hasDeep': function(O, str) {
return !_.isUndefined( _.getDeep(O, str) );
}});

_.isDefined
Because typing !_.isUndefined() all the time is tiresome. Using _.isDefined is clear and more readable.

/**
* Shorthand for !_.isUndefined
* @param {mixed} e Item to be tested
* @return {boolean}
*/
_.mixin({'isDefined': function(e) {
return !_.isUndefined(e);
}});

_.compactObject

/**
* Removes all falsy and undefined values from an object
* @param {object} o Object to be compacted
* @return {object} Compact Object
* @link http://stackoverflow.com/a/14058408/417822
*/
_.mixin({'compactObject': function(o) {
var clone = _.clone(o);

_.each(clone, function(v, k) {
if(!v) delete clone[k];
});

return clone;
}});

_.compactObject

/**
* Toggles an array element
* @param {Array} arr Source Array
* @param {Mixed} val Value to toggle
* @param {Boolean} Optional: Boolean to determine whether to add or remove
* @return {Array} Result
*/
_.mixin({'arrayToggle': function(arr, val, state) {
if ( _.indexOf(arr,val)==-1 || state)
return _.union(arr,[val]);
else
return _.without(arr,val);
}});

Code: Data structure

In my understanding there are different types of data. Each is unique in purpose, mutability, and scope. Clearly identifying the role of an attribute and grouping it with related ones creates a cleaner interface to work with.

Raw Attributes

The raw data that is persisted to the server.

This data should be treated as if immutable, unless planning to persist a change of one of the values to the database. This is the once source of ‘truth’ that is trustworthy. If it is reformatted, or changed it looses its trustworthiness.

user: {
 firstName: 'Phil',
 lastName: 'McCool',
 username: 'pmccool'
}

Computed Values

Take in Raw Data, and reformat it for later use.

More often than not these are a convince to remove the need to repeat logic throughout the app.

If there is an urge to create a value here to describe the model’s content ‘isAdmin’, ‘fullName’, there is a good chance these ought to be part of the data schema to start with.

They can come at a cost of being computed but not always needed everywhere throughout the app. Alternately getter functions could be used to allow a more ‘on-demand’ approach (add result caching and get the both of both worlds).

computed: {
 fullName: 'Phil McCool',
 shortName: 'Phil M.',
 numberVowels: 3
}

State

Describing the state status, of either the data or of the component/view.

State data describes progress or what things are doing currently – [changing, updating, modified]. While these are similar to configuration items, they mutable are more closely tied to the model data describing what is happening to it. If their were multiple components/views that display the same model, they may all want to know the current state of the data. It’s meta data to the data.

These values should update frequently.

state: {
 isLoading: false,
 isModified: true,
 page: 4
}

Configuration

How something should be displayed or behave.

These ought be on the component/view that is rendering the item. It describes the preferences of how something should behave or be displayed. Think of them as options, ways to deviate from the norm, an API for this component/view.

A component/view should have a set of defaults for these values to fall back upon.

Config attributes can make it tempting to overload abstraction. Draw a line of making a new component/view when the core functionality has config options that cause different logic paths.

config: {
 size: 'large',
 template: 'card',
 color: 'blue'
}

 


Take Aways

It can be very tempting to merge or stuff configuration and state data right into the model data. It’s convenient, but lazy. It taints the raw data. If put an ‘isLoading’: true value into our data model then persist it to the server, we ought to feel like we did something wrong.

Ideally we would be able to group data in our actual data structures, but at minimum, we can always just keep in mind the role of an attribute and group mentally.

TL;DR

  • Not all data is alike.
  • Don’t mutate / override original data
  • Computed, State, and Config data shouldn’t be mixed in with raw data.

Code: jquery.otherdropdown.js

Today I published my first node npm package and bower package – jquery.otherdropdown! For quite a while I’ve been reusing a simple code snippet that made it possible for a user to add their own custom response to a select dropdown. I never thought I would publish it.

The principle is simple, in a list of options when the ‘other’ response is selected, prompt the user to specify what they mean. Try out the demo.

jquery.otherdropdown

I’ve seen forms that add an additional input, but it’s effective – but feels choppy to the user. Processing the data can also be slightly more complex when you have to check for a value that may or may not exist.

A long while ago I wrote a script (before jQuery was prevelent) that manipulated the DOM to give the effect I was after. Since then it’s been modified and switched to use jQuery and made it into a plugin.

The functionality is all self contained and pretty simple to use.  Use jQuery to get the select dropdown and runn the plugin on it:

$('.myDropdown').otherdropdown();

Publishing it to Bower I realized could be helpful not only to me but to everyone. Why not give it a go? Many things needed to be done, make it flexible with options for customization, create documentation and demos, and sharpen up the code. After several hours it was ready to go!

It’s been fun to work on. More complex idea are cooking.

Tips: My Favorite Sublime 3 Packages

I primarily use Sublime as my code editor of choice; a bunch of us at Sprout Social do. It’s simple, clean, lightweight on system resources, and it has some pretty sweet packages. I’ve found a number of packages that increase my efficiency developing. Thought I’d share several of these personal favorite Sublime 3 packages.

If you’re on Sublime 2, upgrade to Sublime 3, it’s totally stable.

To get started you’ll need to install Sublime Package Control into Sublime. It’s fairly simple, and the you’re read to go. The “Package Control: Install Package” command will now be available in your command pallet via Cmd+Shift+P or Ctrl+Shift+P.

SublimeLinter

SublimeLinterBase package for all linters. Syntax error highlighting can greatly reduce the save-run-revise cycle time. Most IDEs already have syntax error highlighting, why not add it to Sublime?

There are many SublimeLinter packages. Browse through them find what fits your workflow. Be sure to follow each packages setup instructions, each will be a bit different.

My personal must have’s are:

  1. SublimeLinter-phplint
  2. SublimeLinter-jshint
  3. SublimeLinter-jsxhint
  4. SublimeLinter-csslint
  5. Sublime​Linter-contrib-scss-lint

BracketHighlighter

BracketHighlighterAn even better bracket highlighting than what comes with Sublime. It also shows starting and ending brackets in the gutter, and can matching for [ ], ( ), { }, ” “, ‘ ‘, <tag> </tag>.

SideBarEnhancments

Give the context menu more options when right clicking on files in a project. Duplicate files, move, rename, etc.

DocBlockr

DocBlockrEasier creation of document blocks for functions, classes, methods. It’s intelligent and looks ahead to see what you’re documenting to pre-fill the base info (such as input parameters and what is returned). Documenting is now convenient.

Pro tip: use the Tab key to navigate through the generated documented block, no need to click or use arrow keys.

Shell-Turtlestein

Launch the terminal/command line right in the context of your project directly from Sublime.  Either as a new window or as its own panel within sublime.

GitGutter

Visually shows the diff since the last commit in the gutter.  At a glance you can see what lines are additions, modifications, or deletions.

Origami

Split Sublime into multiple horizontal and vertical panes for side-by-side work. Remove the need to switch between tabs or windows as frequently when comparing files.

TrailingSpaces

Highlights and helps cleanup end of line trailing spaces. Nobody likes them right? Or maybe we just don’t notice them.

 

There are many other great packages out there for Sublime : code snippets, theme,  and syntax highlighting. But these are just some of my favorites.

Code: Laravel Scope Query on a Model

Let’s talk a bit about scoped queries in Laravel. First here is a basic Book Eloquent Model with two handy scopes for type and fewerPagesThan.

//Book Model
class Book extends Eloquent {
public function scopeType( $query, $type ) {
return $query->where( 'books.type', '=', $type );
}

public function scopeFewerPagesThan( $query, $pages ) {
return $query->where( 'books.pages', '<=', $pages ); } }

Using scoping

I often see confusion when we try to use scoping. Some would expect the following to give them back all 'autobiography' books:


Book::type('autobiography'); // This works right? Nope!

But it doesn't. Scoping functions will only refine your query. For instance all the following are great examples of using scoping:


Book::type('autobiography')->get();
Book::with('author')->type('autobiography')->get();
Book::fewerPagesThan(500)->type('autobiography')->get();

Building up scopes

When using scopes to refine and filter down which Models to retrieve, you will always need to add a ->get() at the end. This allows you can chain multiple "scopes" onto each other as in the 3rd example. Basically it needs to know when you are done filtering down and when to actually hit the database.

So the 3rd example could be broken down like this to really drive home the point:


$maxPages = 500;

$books = new Book();
$books->type('autobiography');
if( $maxPages )
$books->fewerPagesThan($maxPages);
$opportunities->get();

In every case before the ->get() call $books var is a Eloquent/Builder that is being built up.

After the ->get() call $books var gets overwritten with an Eloquent/Collection that has been filled with our data from the database.

This is a very powerful and flexible to way to scope and filter down models that are in your database. It is better to filter them down with scopes in the DB query than filter down a collection that has already been loaded into memory. Make the your DB do some weight lifting for you. 😉

Utility: Bootable ISO on USB Drive

I’ve given up burning ISOs to a disc. CDs are in the past. It took time to burn them, store them, and find them. I have all my CDs/DVDs in ISO form using another awesome lightweight utility that creates ISOs.

YUMI – Multiboot USB Creator

YUMI is a utility I’ve been using to load ISOs to a bootable USB disk.  The process is pretty dead simple and takes but a few moments to transfer an image to the USB disk.

  1. Choose the destination USB Device
  2. The type of ISO
  3. The source .iso file

YUMI-Multiboot-USB-Creator

Removing ISOs is equally simple via the View and Remove Installed Distors.

YUMI-Boot-Menu

Providing your system has the proper boot order to allow booting from a USB, YUMI will startup and ask what ISO you wish to launch. From there – business as usual.

Download

YUMI.exe (1.2MB)
Developer’s Site

 

A place for collecting my miscellaneous thoughts.