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JavaScript Tutorial Series - Promises

on May 07, 2020

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JavaScript Tutorial Series - Exceptions

In JavaScript, errors can be caught using exception handling. Exception handling will prevent an application from crashing and not being able to recover. Exception handling is a much cleaner way than the old fashioned way of setting up your own error codes, passing them around and doing comparisons. Exception handling is implemented using try catch blocks. The try statement encloses a block of code to run. The catch captures runtime errors that occurred within the code block. Captures contain code to handle what to do when errors occur. Finally blocks are optional and contain a block of code that always runs after the try/catch, whether or not an error occurred. Throw statements are custom errors sent from a block of code to the block of code that called it. The first try/catch encountered in the calling chain will handle the error. The throw statement can throw a string, number, boolean or object. The throw statement can be used as follows: function addNumbers(a, b) { if (ty...

JavaScript Tutorial Series - Loops

Loops are used to run a block of code multiple times. JavaScript supports while loops, do while loops and several types of for loops. While loops run a block of code until a condition is no longer true. A while loop condition needs to be carefully written. If the condition never fails, the loop will never stop. It will become an infinite loop that will hang the program and make it unresponsive. The following is an example of an infinite loop, so don't do this: let i = 0; while (i This is an infinite loop because the i variable never changes. This loop is fixed by incrementing i as follows: let i = 0; while (i JavaScript also supports do while loops. This type of loop always executes once. Any further executions are dependent on the while condition. Example: do { let i = 0; console.log('i: ' + i); i++; } while (i For loops run a block of code a given number of times. A for loop sets a variable to a start number. It has a conditional that compa...

JavaScript Tutorial Series - Functions

Functions are used to enclose a block of code which performs a single task. Functions should be kept fairly small. If a function gets too large, that could be a sign it is doing more than a single task and should be broken down into multiple functions, each doing a different task that when used together, perform the main task. Functions may return values by using the return keyword. In JavaScript, functions may be written in several ways. One way is to use the function keyword: function wearAJacket(temperature) { if (temperature This is called a function declaration. The above function defines a function with the name wearAJacket. A variable called temperature is passed in to it. The statements inside the function perform a test using if functions to determine if the caller should wear a jacket or not. The function returns true if the temperature value is below a predefined threshold, false otherwise. Function declarations are hoisted to the top of the code it is contai...

JavaScript Tutorial Series - Set Up

JavaScript runs in a web browser, so all that is needed to get started is having a web browser, such as Google Chrome, Firefox or Internet Explorer, etc. installed on your computer. That's it. Super simple. Implementation: The goal of this JavaScript Tutorial series is to teach JavaScript to someone with programming knowledge. This tutorial will help you create a basic website using HTML and CSS that has JavaScript added to it to for dynamic functionality. The JavaScript will call a REST api and use the returned data to display the user's current weather on the webpage. Don't worry if you don't know HTML or CSS. Those pieces will be minimal. The focus will be on JavaScript. The first step in the tutorial is to create a directory on your computer where the tutorial files will live. Once that directory is made, add a file called index.html. Add a directory called css. Inside it create an empty file called style.css. Create another directory called js. Inside it crea...

JavaScript Tutorial Series - Arrays

In JavaScript, arrays store a list of items. An item may be a primitive such as a string or number. An item may also be an object or another array. Indexing starts at 0. Arrays are objects. To determine if a variable is an array, use Object.prototype.toString.call(theArray) === '[object Array]' or the newer way of Array.isArray(theArray); Some of the more commonly used actions that may be performed on an array include: Initialize: let myArray = ['a', 'b', 'c']; Arrays can be created by calling: let myArray2 = new Array('a', 'b', 'c'); The first way is much simpler, so there's not really any reason to use this way. To retrieve the number of items in the list, do the following: let count = myArray.length; Individual items in an array may be accessed by it's index. To access the first item, call let firstItem = myArray[0]; To access the last item, call let last...

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