Javascript notes pdf free download

Sometimes, you may get business requirement where you need to allows users to enter only numbers, we can do JavaScript number validation very easily. Sometimes, you may get business requirement where you need to allows users to enter either letter and numbers, we can validate letters and numbers by using JavaScript very easily. We can retrive current date, current month, current year, curren time from Date using JavaScript. We use arrays in JavaScript to store multiple values.

We can easily reverse an array using JavaScript by using reverse method. Now we will see how we can concate or merge two arrays in JavaScript by using the concat method. We can open a new web page using window. If the condition is false, another block of code can be executed. We can print a page using window. Here once the user clicks on the button, Print setup page will appear. This JavaScript example, we will see how we can insert an element into an array in JavaScript.

We can use the Push method to insert an element to an array in JavaScript. We can get currrent url using JavaScript by using the window. In an alert box, we are displaying the value from a class div. Here I am trying to check a checkbox based on the name attribute which we retrieve getElementByName method. By using JavaScript, we can easily disable browser back and forward button. We can use window. By using window. We can easily enable or disable dropdown list using JavaScript by using disabled property.

Below is the JavaScript code which we can use to enable dropdown list. We can enable dropdown list by simply setting disabled property to false. Below is the PowerShell script, by using which we can disable mouse right click using JavaScript. We can display a javascript date countdown timer using javascript easily. Below is a timer example in JavaScript. This example shows how to check checkbox is checked or not in javascript.

For this example, on a button click we are displaying if a check box is checked or not. Or we can get url parameter value by name using javascript. You can see below example, by clicking on a button video is playing and in another button click video we are pausing the video using JavaScript. In JavaScript, we can easily get max number in an array of objects. Below is the code which will give the max number in the array. Below JavaScript examples, it shows how to sort and reverse an array of objects in JavaScript by using the sort and reverse method.

This JavaScript example explains how to use try and catch in JavaScript. Try catch block is necessary for catching errors in JavaScript code. This JavaScript example shows how we can return boolean value of an integer express in JavaScript. We can check an object is an array or not in JavaScript by using the isArray method.

The isArray method output will display true or false value. We can display tooltip messages on mouse over in JavaScript. Below is the JavaScript code which will display tooltip message in JavaScript. Reload is nothing but a method is used to reload the curent document.

Below is the JavaScript code which will reload a page on button click. Once you click on the button, it will reload the page. This javascript example explains how to use conditional operator. This JavaScript example explains how we can set dropdown value on button click. Here I have a dropdown list which has some values and on one button click I will set a particular value using JavaScript. Most work with 2 operands. Just one operator works with 3 operands. In this first introduction to operators, we'll introduce the operators you are most likely familiar with: operators with 2 operands.

Let's now introduce another set of binary operators that you're already familiar with from basic math. If you divide by zero, JavaScript does not raise any error but returns the Infinity value or -Infinity if the value is negative. A remainder by zero is always NaN , a special value that means "Not a Number":. Every complex statement with multiple operators in the same line will introduce precedence problems.

Some operations have more precedence than the others. The precedence rules are listed in this table:. After assignment and math operators, the third set of operators I want to introduce is conditional operators. Comparison operators always return a boolean, a value that's true or false. In addition to those, we have 4 equality operators. They accept two values, and return a boolean:. An if statement is used to make the program take a route, or another, depending on the result of an expression evaluation.

The conditional checks the expression you pass to it for a true or false value. If you pass a number, that always evaluates to true unless it's 0. If you pass a string, it always evaluates to true unless it's an empty string. Those are general rules of casting types to a boolean. Did you notice the curly braces? That is called a block , and it is used to group a list of different statements. A block can be put wherever you can have a single statement. And if you have a single statement to execute after the conditionals, you can omit the block, and just write the statement:.

The first is using the array literal syntax. The second uses the Array built-in function. Since we can add an array into an array, we can create multi-dimensional arrays, which have very useful applications e.

You can initialize a new array with a set of values using this syntax, which first initializes an array of 12 elements, and fills each element with the number 0 :. Note that you can set the length of the array. If you assign a bigger number than the arrays current capacity, nothing happens. If you assign a smaller number, the array is cut at that position:.

Returns the first item that returns true, and returns undefined if the element is not found. I personally prefer single quotes all the time, and use double quotes only in HTML to define attributes. Another way to define strings is to use template literals, defined inside backticks. They are especially useful to make multiline strings much simpler.

With single or double quotes you can't define a multiline string easily - you'd need to use escaping characters. Once a template literal is opened with the backtick, you just press enter to create a new line, with no special characters, and it's rendered as-is:.

Template literals are also great because they provide an easy way to interpolate variables and expressions into strings. With a loop we can automate and repeat a block of code however many times we want it to run, even indefinitely. We add a condition after the while keyword, and we provide a block that is run until the condition evaluates to true.

Very similar to while , we have do.. It's basically the same as while , except the condition is evaluated after the code block is executed. We use the for keyword and we pass a set of 3 instructions: the initialization, the condition, and the increment part.

Just like with while loops, you can interrupt a for loop using break and you can fast forward to the next iteration of a for loop using continue.

This loop is relatively recent introduced in and it's a simplified version of the for loop:. Note that in the second invokation I passed the black string parameter as the color argument, but no age. In this case, age inside the function is undefined. Although the conditional will also be true if age is null , 0 or an empty string. You can pass any value as a parameter: numbers, strings, booleans, arrays, objects, and also functions.

A function has a return value. By default a function returns undefined , unless you add a return keyword with a value:. They are very often used instead of "regular" functions, the ones I described in the previous chapter. You'll find both forms used everywhere.

If the function body contains just a single statement, you can omit the parentheses and write everything on a single line:. Arrow functions allow you to have an implicit return - values are returned without having to use the return keyword. Like with regular functions, we can have default values for parameters in case they are not passed:. The two types of functions are very similar, so you might ask why arrow functions were introduced.

The big difference with regular functions is when they are used as object methods. This is something we'll soon look into. Any value that's not of a primitive type a string, a number, a boolean, a symbol, null, or undefined is an object. This is the object literal syntax, which is one of the nicest things in JavaScript.

You can also initialize an object using the new keyword before a function with a capital letter. This function serves as a constructor for that object. In there, we can initialize the arguments we receive as parameters, to setup the initial state of the object:. If you assign a variable the same value of another, if it's a primitive type like a number or a string, they are passed by value:.

Even arrays or functions are, under the hood, objects, so it's very important to understand how they work. The value of a property can be of any type, which means that it can be an array, a function, and it can even be an object, as objects can nest other objects. Here we have a car object with a property named color , with value blue. Labels can be any string, but beware of special characters - if I wanted to include a character not valid as a variable name in the property name, I would have had to use quotes around it:.

The second which is the only one we can use for properties with invalid names , is to use square brackets:. Functions can be assigned to a function property, and in this case they are called methods. In this example, the start property has a function assigned, and we can invoke it by using the dot syntax we used for properties, with the parentheses at the end:. In the following example, we have access to the brand and model properties values using this.

It's important to note this distinction between regular functions and arrow functions - we don't have access to this if we use an arrow function:. We can create a class named Person note the capital P , a convention when using classes , that has a name property:. There is a special method called constructor that we can use to initialize the class properties when we create a new object instance.

Now we can instantiate a new object from the class, pass in a string, and when we call hello we'll get a personalized message:. When the object is initialized, the constructor method is called with any parameters passed.

A class can extend another class, and objects initialized using that class inherit all the methods of both classes. Now if we instantiate a new object with the class Programmer , it has access to the hello method:. One of the simplest examples of how to use callbacks is with timers. Timers are not part of JavaScript, but they are provided by the browser and Node. Let me talk about one of the timers we have: setTimeout.

The setTimeout function accepts 2 arguments: a function, and a number. The number is the milliseconds that must pass before the function is ran. The function containing the console. If you add a console. This is a very common pattern when working with the file system, the network, events, or the DOM in the browser. As we saw in the previous chapter, with callbacks we'd be passing a function to another function call that would be called when the function has finished processing.

The main problem with this approach is that if we need to use the result of this function in the rest of our code, all our code must be nested inside the callback, and if we have to do callbacks we enter in what is usually defined "callback hell" with many levels of functions indented into other functions:. We first call the function, then we have a then method that is called when the function ends.

Now, to be able to use this syntax, the doSomething function implementation must be a little bit special. It must use the Promises API. While it will be of particular value to people with no programming experience,even people who have used other. As of today we have 76,, eBooks for you to download for free. No annoying ads, no download limits, enjoy it and don't forget to bookmark and share the love! CS Lecture Notes - JavaScript Programming Object-oriented programming: inheritance Javascript has the notion of a prototype object for each object instance Prototype objects can have prototype objects forming a prototype chain On an object property read access JavaScript will search the up the prototype chain until the property is found.