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Resilient Web Design By Jeremy Keith HTML Rather than being a guide to solid web design, Resilient Web Design has been written to highlight some of the approaches and techniques to web design that have proven to be resilient over the years. It includes chapters on the box model, layout, tables, color, typography, and transitions, and does include interactive examples.
Please note that you will need to signup to download this ebook. The book has been organized into 2 sections: First, there are the reading portions where it describes how an API works with interactive examples , and then there are the hands-on lessons that will walk you through the process of building your own canvas apps. The free online version includes 53 interactive examples and exercises. It has been written for designers and developers that are looking to quickly add SVG to their workflow.
Developing Backbone. This must stop. It is available as a PDF file, so you can easily download it and use it as per your convenience. In any case, the prototype of car is Object: If you initialize an array, which is an object: The prototype is Array. You can verify this by checking the Object. All the properties and methods of the prototype are available to the object that has that prototype: The above example you saw is an example of the prototype chain at work.
I can make an object that extends Array and any object I instantiate using it, will have Array and Object in its prototype chain and inherit properties and methods from all the ancestors. In addition to using the new operator to create an object, or using the literals syntax for objects and arrays, you can instantiate an object using Object.
The first argument passed is the object used as prototype: You can check the prototype of an object using the isPrototypeOf method: Pay attention because you can instantiate an array using.
When the object is initialized, the constructor method is called, with any parameters passed. A class also has as many methods as it needs. In this case hello is a method and can be called on all objects derived from this class: A class can extend another class, and objects initialized using that class inherit all the methods of both classes. If the inherited class has a method with the same name as one of the classes higher in the hierarchy, the closest method takes precedence: I am a programmer.
Some prefer to use them always, no matter what. Others like to avoid them. After using semicolons for years, in the fall of I decided to try avoiding them as needed, and I did set up Prettier to automatically remove semicolons from my code, unless there is a particular code construct that requires them.
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Introduced in ES, aka ES6, Template Literals offer a new way to declare strings, but also some new interesting constructs which are already widely popular. The syntax at a first glance is very simple, just use backticks instead of single or double quotes: They are unique because they provide a lot of features that normal strings built with quotes, in particular: Template literals make multiline strings much simpler.
Keep in mind that space is meaningful, so doing this: Is going to create a string like this: An easy way to fix this problem is by having an empty first line, and appending the trim method right after the closing backtick, which will eliminate any space before the first character: Template literals provide an easy way to interpolate variables and expressions into strings.
The styled. This function returns a string, which can be the result of any kind of computation. The first is something , the string until the first interpolation, and the second is an empty string, the space between the end of the first interpolation we only have one and the end of the string.
The function that is passed those values can do anything with them, and this is the power of this kind of feature. The most simple example is replicating what the string interpolation does, by simply joining literals and expressions: A function is a block of code, self contained, that can be defined once and run any number of times you want.
Functions can be assigned to variables this is called a function expression: Named function expressions are similar, but play nicer with the stack call trace, which is useful when an error occurs - it holds the name of the function: ES introduced trailing commas for parameters, a feature that helps reducing bugs due to missing commas when moving around parameters e. You can wrap all your arguments in an array, and use the spread operator when calling the function: With many parameters, remembering the order can be difficult.
The nested function is scoped to the outside function, and cannot be called from the outside. Consider this example: This is because the handling of this is different in the two functions declarations style. This implies that arrow functions are not suitable to be used for object methods and constructors arrow function constructors will actually raise a TypeError when called.
They slightly differ from regular functions. I already introduced arrow functions above, but they are so important they need their own section. In my opinion this change was so welcome that you now rarely see in modern codebases the usage of the function keyword. If the function body contains just a single statement, you can omit the parentheses and write all on a single line: If you have one and just one parameter, you could omit the parentheses completely: Thanks to this short syntax, arrow functions encourage the use of small functions.
Arrow functions allow you to have an implicit return: Another example, returning an object remember to wrap the curly brackets in parentheses to avoid it being considered the wrapping function body brackets: When defined as a method of an object, in a regular function this refers to the object, so you can do: The this scope with arrow functions is inherited from the execution context.
An arrow function does not bind this at all, so its value will be looked up in the call stack, so in this code car.
Arrow functions cannot be used as constructors as well, when instantiating an object. It will raise a TypeError. This is where regular functions should be used instead, when dynamic context is not needed.
This is also a problem when handling events. DOM Event listeners set this to be the target element, and if you rely on this in an event handler, a regular function is necessary: As you can see, the state of the variable say is linked to the function that's returned from prepareBark. Also notice that we redefine a new say variable the second time we call prepareBark , but that does not affect the state of the first prepareBark scope. This is how a closure works: This section aims to explain what you should use, as of Iterates a and builds a new array with the result of executing f on each a element.
Iterates a and builds a new array with elements of a that returned true when executing f on each a element. If initialValue is specified, accumulator in the first iteration will equal to that value.
Introduced in ES5. Given an array, you can iterate over its properties using list.
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You can listen on window to intercept "global" events, like the usage of the keyboard, and you can listen on specific elements to check events happening on them, like a mouse click on a button. Other properties are provided by specific kind of events, as Event is an interface for different specific events: For example when a KeyboardEvent happens, you can check which key was pressed, in a readable format Escape , Enter and so on by checking the key property: You want to track when users click on the button, and you have two event listeners, one on button , and one on container.
Bubbling means that the event propagates from the item that was clicked the child up to all its parent tree, starting from the nearest one.
In our example, the handler on button will fire before the container handler. Capturing is the opposite: You can choose to adopt event capturing by applying a third argument to addEventListener, setting it to true: The order follows this principle: While doing so, it calls any event handler associated with the event capturing phase.
Once it reaches the target, it then repeats the journey up to the parents tree until the Window object, again calls the event handlers bubbling phase. A click event on a will propagate to section and then body. You can stop the propagation by calling the stopPropagation method of an Event, usually at the end of the event handler: Of course in this case click is fired just before this event. Be careful with mousemove , as it fires many times during the mouse movement see throttling later. The scroll event is fired on window every time you scroll the page.
Inside the event handler you can check the current scrolling position by checking window. Keep in mind that this event is not a one-time thing. As we mentioned above, mousemove and scroll are two events that are not fired one-time per event, but rather they continuously call their event handler function during all the duration of the action.
If you perform a complex operation in the event handler, you will affect the performance and cause a sluggish experience to your site users.
In general, in most browsers there is an event loop for every browser tab, to make every process isolated and avoid a web page with infinite loops or heavy processing to block your entire browser. The environment manages multiple concurrent event loops, to handle API calls for example. Web Workers run in their own event loop as well.
You know the error stack trace you might be familiar with, in the debugger or in the browser console? The browser looks up the function names in the call stack to inform you which function originates the current call: When this code runs, first foo is called. Inside foo we first call bar , then we call baz.
The Message Queue is also where user-initiated events like click or keyboard events, or fetch responses are queued before your code has the opportunity to react to them. Or also DOM events like onLoad. For example, if you set the setTimeout timeout to 2 seconds, you don't have to wait 2 seconds - the wait happens elsewhere.
This means that code cannot create new threads and run in parallel. In the current consumer computers, every program runs for a specific time slot, and then it stops its execution to let another program continue its execution. When a program is waiting for a response from the network, it cannot halt the processor until the request finishes.
Normally, programming languages are synchronous, and some provide a way to manage asynchronicity, in the language or through libraries. Some of them handle async by using threads, spawning a new process.
How could it do this with a synchronous programming model? The answer was in its environment. The browser provides a way to do it by providing a set of APIs that can handle this kind of functionality.
More recently, Node.
One very common strategy is to use what Node. If there is no error, the object is null. If there is an error, it contains some description of the error and other information.
Promises are one way to deal with asynchronous code, without writing too many callbacks in your code. Although being around since years, they have been standardized and introduced in ES, and now they have been superseded in ES by async functions. Once a promise has been called, it will start in pending state. This means that the caller function continues the execution, while it waits for the promise to do its own processing, and give the caller function some feedback.
At this point, the caller function waits for it to either return the promise in a resolved state , or in a rejected state , but the function continues its execution while the promise does its work. In addition to your own code and libraries code, promises are used by standard modern Web APIs such as: As you can see the promise checks the done global constant, and if that's true, we return a resolved promise, otherwise a rejected promise.
Using resolve and reject we can communicate back a value, and in the above case we just return a string, but it could be an object as well. Running checkIfItsDone will execute the isItDoneYet promise and will wait for it to resolve, using the then callback, and if there is an error, it will handle it in the catch callback. The Fetch API is a promise-based mechanism, and calling fetch is equivalent to defining our own promise using new Promise. In this example, we call fetch to get a list of TODO items from the todos.
Running fetch returns a response , which has many properties, and within those we reference: So given those premises, this is what happens: This operation will cause the promise chain to skip all the chained promises listed and will skip directly to the catch statement at the bottom, logging the Request failed text along with the error message.
If that succeeds instead, it calls the json function we defined. Since the previous promise, when successful, returned the response object, we get it as an input to the second promise. In the example, in the previous section, we had a catch that was appended to the chain of promises.
When anything in the chain of promises fails and raises an error or rejects the promise, the control goes to the nearest catch statement down the chain. If inside the catch you raise an error, you can append a second catch to handle it, and so on. If you need to synchronize different promises, Promise. You are not limited to using fetch of course, any promise is good to go. Async functions are a combination of promises and generators, and basically, they are a higher level abstraction over promises.
Let me repeat: When Promises were introduced in ES, they were meant to solve a problem with asynchronous code, and they did, but over the 2 years that separated ES and ES, it was clear that promises could not be the final solution. Promises were introduced to solve the famous callback hell problem, but they introduced complexity on their own, and syntax complexity.
They were good primitives around which a better syntax could be exposed to the developers, so when the time was right we got async functions. When you want to call this function you prepend await , and the calling code will stop until the promise is resolved or rejected. One caveat: Here's an example: Prepending the async keyword to any function means that the function will return a promise. As you can see in the example above, our code looks very simple.
Compare it to code using plain promises, with chaining and callback functions. And this is a very simple example, the major benefits will arise when the code is much more complex. Async functions can be chained very easily, and the syntax is much more readable than with plain promises: Debugging promises is hard because the debugger will not step over asynchronous code.
This function simply console logs the loop index variable i. Since var declarations are hoisted , the above code equals to. So, in the for-of loop, i is still visible, it's equal to 5 and every reference to i in the function is going to use this value.
The simplest solution is to use let declarations. Introduced in ES, they are a great help in avoiding some of the weird things about var declarations. Simply changing var to let in the loop variable is going to work fine: How is this possible? This works because on every loop iteration i is created as a new variable each time, and every function added to the operations array gets its own copy of i.
This is the job of setTimeout. You specify a callback function to execute later, and a value expressing how later you want it to run, in milliseconds: This syntax defines a new function. You can call whatever other function you want in there, or you can pass an existing function name, and a set of parameters: This is generally not used, but you can store this id, and clear it if you want to delete this scheduled function execution: If you specify the timeout delay to 0 , the callback function will be executed as soon as possible, but after the current function execution: This is especially useful to avoid blocking the CPU on intensive tasks and let other functions execute while performing a heavy calculation, by queuing functions in the scheduler.
The function above runs every 2 seconds unless you tell it to stop, using clearInterval , passing it the interval id that setInterval returned: For example this code runs something unless App.
Maybe the function takes different execution times, depending on network conditions for example: To avoid this, you can schedule a recursive setTimeout to be called when the callback function finishes: Outside any object, this in strict mode is always undefined.
Strict Mode mostly removes functionality that was possible in ES3, and deprecated since ES5 but not removed because of backwards compatibility requirements.
An Immediately-invoked Function Expression is a way to execute functions immediately, as soon as they are created. We basically have a function defined inside parentheses, and then we append to execute that function: Those wrapping parentheses are actually what make our function, internally, be considered an expression.
A reminder by zero is always NaN , a special value that means "Not a Number": Increment a number. This is a unary operator, and if put before the number, it returns the value incremented. If the operand is not a number, it tries to convert it. Otherwise if the operand is already a number, it does nothing.
The result is 2. What operations are executed first, and which need to wait? Some operations have more precedence than the others. The precedence rules are listed as follows: The Math object contains lots of utilities math-related. While Node. Every major decision such as a module system must be first standardized by ECMAScript and then implemented by the browser.
In this example, the uppercase. You can also use an absolute path for the module import, to reference modules defined on another domain: This creates one default export. In a file however you can export more than one thing, by using this syntax: You can import the default export, and any non-default export by name, like in this common React import: You can check an ES Modules example on https: Modules are fetched using CORS.
This means that if you reference scripts from other domains, they must have a valid CORS header that allows cross-site loading like Access-Control-Allow-Origin: ES Modules are one of the biggest features introduced in modern browsers. They are part of ES6 but the road to implement them has been long. We can now use them! Webpack is probably going to still be a huge player even if ES Modules land in the browser, but having such a feature directly built in the language is huge for a unification of how modules work in the client-side and on Node.
The typical example is an AJAX call, which might take even seconds and in the meantime you complete other stuff, and when the response is ready, the callback function gets called. An if statement contains a block, a for loop contains a block. With Function Scoping, any variable defined in a block is visible and accessible from inside the whole block, but not outside of it. A declarative approach is when you tell the machine what you need to do, and you let it figure out the details.
React is considered declarative, as you reason about abstractions rather than editing the DOM directly. Every high level programming language is more declarative than a low level programming language like Assembler.
Or for a browser that has not implemented an API, you should have a fallback to avoid completely breaking the experience of the user. With Function Scoping, any variable defined in a function is visible and accessible from inside the whole function.
We basically have a function defined inside parentheses, and then we append to execute that function: Map and Set and their respective garbage collected WeakMap and WeakSet are the official implementations of two very popular data structures introduced later on. Default to const , and only use let if you reassign the variable.
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