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To check if a JavaScript function is defined or not, checks it with “undefined”.ExampleYou can try to run the following example to check for a function is defined or not in JavaScript − function display() { alert("Demo Text!"); } if ( typeof(display) === 'undefined') { document.write('undefined'); } else { document.write("Function is defined"); }
To debug JavaScript in Visual Studio, follow the below-given steps −Open Visual StudioSelect your project to be debugged in Solution Explorer.Right Click and select Browse With, and set a default browser.Now, go to START and type Internet Options.Above, uncheck both the options for Disable script debugging.Click Apply, and then Ok.Now set breakpoints in your JS file.After that press the debug button in Visual Studio.
The following are some of the common HTML events supported by JavaScript −AttributeValueDescriptiononclickscriptTriggers on a mouse clickoncontextmenuscriptTriggers when a context menu is triggeredondblclickscriptTriggers on a mouse double-clickondragscriptTriggers when an element is draggedondragendscriptTriggers at the end of a drag operationondragenterscriptTriggers when an element has been dragged to a valid drop targetondragleavescriptTriggers when an element is being dragged over a valid drop targetondragoverscriptTriggers at the start of a drag operationondragstartscriptTriggers at the start of a drag operationondropscriptTriggers when dragged element is being droppedondurationchangescriptTriggers when the length of the media is changed
JavaScript Identifiers are names given to variables, functions, etc. It is the same as identifiers in other programming languages like C, C++, Java, etc. Let’s see identifiers for variable names.The following are legal variable names −val val1 resultWhile naming your variables in JavaScript, keep the following rules in mind.You should not use any of the JavaScript reserved keywords as a variable name. These keywords are mentioned in the next section. For example, break or boolean variable names are not valid.JavaScript variable names should not start with a numeral (0-9). They must begin with a letter or an underscore character. For ... Read More
To get started with Node.js, you need to first set its environment. If you are still willing to set up your environment for Node.js, you need the following two software available on your computer, (a) Text Editor and (b) The Node.js binary installable.Let’s see how to install Node.js binary distribution on Windows. Download the latest version of Node.js installable archive file from Node.js official website.Use the MSI file and follow the prompts to install the Node.js. By default, the installer uses the Node.js distribution in “C:\Program Filesodejs”. The installer should set the “C:\Program Filesodejs\bin” directory in the window's PATH environment variable. ... Read More
To launch JavaScript debugger in Google Chrome, try any of the following ways,Press Ctrl + Shift + JGo to Settings and click More Tools. After that, click Developer Tools.For more, refer the official website of Chrome Dev Tool,
Use throw statement in JavaScript, to catch custom exceptions. You can try to run the following to work with custom exceptions −Example Click the following to see the result:
To catch all JavaScript unhandled exceptions, use window.error. The onerror event handler provides three pieces of information to identify the exact nature of the error −Error message − The same message that the browser would display for the given errorURL − The file in which the error occurredLine number− The line number in the given URL that caused the errorExampleYou can try to run the following code to catch unhandled exceptions − Click the following to see the result:
To learn how to define and implement custom JavaScript exceptions, you can try to run the following code −Example Click the following to see the result:
When a function is passed to another function, it is called a callback function. It goes over this function than to call a passed function.ExampleYou can try to run the following code to learn how to work with callback functions − var callback = function(myCallback) { setTimeout(function() { myCallback(); }, 5000); }; document.write("First is displayed"); document.write("Second is displayed"); callback(function() { document.write("This is Callback function"); }); document.write("Last is displayed");