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Front End Technology Articles
Page 523 of 652
How do you check that a number is NaN in JavaScript?
NaN is a JavaScript property, which is Not-a-Number value. This shows it is not a legal number. Here’s the syntax −SyntaxNumber.NaNTo find out whether a number is NaN, use the Number.isNaN() or isNan() method. Here’s an example to check −ExampleLive Demo Check function display() { var a = ""; a = a + isNaN(434) + ": 434"; a = a + isNaN(-23.1) + ": -23.1"; a = a + isNaN('Hello') + ": 'Hello'"; a = a + isNaN(NaN) + ": NaN"; a = a + isNaN('') + ": ''"; a = a + isNaN(0) + ": 0"; a = a + isNaN(false) + ": false"; document.getElementById("test").innerHTML = a; }
Read MoreHow to calculate the difference between two dates in JavaScript?
To get dates in JavaScript, use the getTime() method. Forgetting the difference between two dates, calculate the difference between date and time.ExampleYou can try to run the following code to learn how to calculate a difference between two dates −Live Demo var dateFirst = new Date("11/25/2017"); var dateSecond = new Date("11/28/2017"); // time difference var timeDiff = Math.abs(dateSecond.getTime() - dateFirst.getTime()); // days difference var diffDays = Math.ceil(timeDiff / (1000 * 3600 * 24)); // difference alert(diffDays);
Read MoreHow to get a number value of a string in Javascript?
To get an integer in the string “abcde 30”, use the following regex in JavaScript, else it will return NaN. With that, use parseInt() to get the numbers with regex under String match() method −ExampleLive Demo var myStr = "abcdef 30"; var num = parseInt(myStr.match(/\d+/)) alert(num);
Read MoreHow to get a string representation of a number in JavaScript?
Use the toString() method to get the string representation of a number. You can try to run the following code to print a string representation of numbers like 20, -40, 15.5 −ExampleLive Demo var num1 = 25; document.write(num1.toString()+""); document.write((30.2).toString()+""); var num2 = 3; document.write(num2.toString(2)+""); document.write((-0xff).toString(2)); Output25 30.2 11 -11111111Above, you can see we added a parameter to the toString() method. This is an optional parameter, which allows you to add an integer between 2 and 36, which is the base for representing numeric values.
Read MoreHow to use the 'with' keyword in JavaScript?
The with keyword is used as a kind of shorthand for referencing an object's properties or methods.The object specified as an argument to with becomes the default object for the duration of the block that follows. The properties and methods for the object can be used without naming the object.SyntaxThe syntax for with object is as follows −with (object){ properties used without the object name and dot }ExampleYou can try to learn the following code to learn how to implement with keyword −Live Demo User-defined objects ...
Read MoreWhat is the difference between new operator and object() constructor in JavaScript?
The new operatorThe new operator is used to create an instance of an object. To create an object, the new operator is followed by the constructor method.In the following example, the constructor methods are Object(), Array(), and Date(). These constructors are built-in JavaScript functions.var department = new Object(); var books = new Array("C++", "Perl", "Java"); var day = new Date(“December 1, 2017");The object() constructorA constructor is a function that creates and initializes an object. JavaScript provides a special constructor function called Object() to build the object. The return value of the Object() constructor is assigned to a variable.The variable contains ...
Read MoreHow can I pop-up a print dialog box using JavaScript?
To pop-up a print dialog box using JavaScript, use the print() method. With the dialog box, you can easily set the printing options like which printer to select for printing.This is the dialog box −ExampleYou can try to run the following code to learn how to print a page −Live Demo Click to Print function display() { window.print(); }
Read MoreHow do I print a message to the error console using JavaScript?
To print a message to the error console, use the console object. Here’s an example −The following will show a red error message −console.error(message);The following gives you the default message −console.log(message);The following gives you the warning message −console.warn(message);The following gives an information message −console.info(message);Add CSS to the log message −console.log('%c Add message!, "background: green; color: white;");Use the following to print error. Consider “num” as the variable name −console.error('num=%d', num);For complete API reference, refer Console API Reference.
Read MoreHow to create JavaScript objects using new operator?
The new keyword in JavaScript is the new operator, which creates an instance of a user-defined object type.ExampleYou can try to run the following code to create JavaScript objects using new operator −Live Demo var dept = new Object(); dept.employee = "Amit"; dept.department = "Technical"; dept.technology ="Java"; document.getElementById("test").innerHTML = dept.employee + " is working on " + dept.technology + " technology."; OutputAmit is working on Java technology.
Read MoreHow I can set the width and height of a JavaScript alert box?
To set the width and height of an alert box in JavaScript, you need to use the custom alert box. This alert box is styled with CSS.Set the width and height of the alert box using the following code, which uses jQuery, a JavaScript library −Example function functionAlert(msg, myYes) { var confirmBox = $("#confirm"); confirmBox.find(".message").text(msg); confirmBox.find(".yes").unbind().click(function() ...
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